Introduction 

When you're playing an archer, or a warrior, your character's strength is expressed in a few ways. You level up skills, select perks, and loot better equipment. This means that you need to explore to deal more damage or absorb more.
For a mage, your progression is more limited: your skills only make your spells stronger, and higher level spells can only be obtained from spell vendors. High level spell tomes are unable to be found in the overworld. Enchantments help, but they are not limited to mage characters.
This discrepancy made the character progression for my mage playthroughs extremely boring and one-sided.

First of all, This mod adds adept and expert level spell tomes to loot lists. You can now find these items in loot, boss chests, whatever. These lists are unleveled and are entirely handled by chance. This means that a patch with Morrowloot or Skyrim Unleveled, or probably even Requiem, is unnecessary. To prevent any old chum from getting their hands on a super strong spell early on, I've done something else, too.
This mod adds new objects to the game that you need to have in your inventory in order to be able to cast adept level spells and up.
Expert level spells are also about 30% cheaper, for reasons i'll explain in a different section.
These items can be found in boss chests, in certain hand-placed locations (a lot of dungeons have at least one spawn of these items) and very rarely on slain mages or vampires.
If you lack the required items for a spell, your spell cost is roughly tripled. This is true for adept level and expert level spells only. Novice, apprentice and master spells are unaffected by this mod, because a mage character would need to have some firepower, and also a feasible goal to work towards.

Just getting any special item introduced by this mod won't do, though. You would need to get the correct one.
For adept level spells, there are five items, each pertaining to a school of magic. These objects are called catalysts. If you have a destruction catalyst, for example, you will be able to cast adept-level spells without any penalties. If not, the aforementioned debuff is activated.
Expert level spells are significantly more powerful and thus require more items to be able to be cast. The expert spells are also the main reason why I developed this mod. Of course, you would need a catalyst for each respective school of magic, just like with adept level spells. However, for expert level spells you need a high catalyst. If you have a high catalyst in your inventory you will also be able to cast adept level spells freely. This is done to prevent character-hampering results from bad rolls on the loot: you might get showered with high catalysts when you really would need normal ones, as your character would not know any expert-level spells at that point in time.
Adept-level items are more common than their expert-level counterparts.

All this catalyst talk might sound very confusing but it gets better. For expert-level spells you need another item, a so-called enigma. These mysterious objects are also required for expert level spells to be cast: only a high catalyst won't do. Enigmas pertain to the genre of magic in a certain school a certain spell is in. What is a genre, you may ask? For destruction it's an element, such as fire. The spell "Incinerate" would, for example, need both a high desctruction catalyst and a fire enigma to be in the player's inventory to be able to be cast without debuffs. Other schools follow the same pattern: expert level anti-undead spells and healing spells from the restoration school both have their own enigma and as a result need these items, as well as a high restoration catalyst, to be in their inventory.

I'm gonna make a short list to illustrate what I've explained here.

ADEPT LEVEL SPELLS NEED:
A catalyst. For example, Close Wounds needs:

• a Restoration Catalyst.
  

Fireball needs:

• a Destruction Catalyst.
  

And so on.
EXPERT LEVEL SPELLS NEED:
A high catalyst and an enigma. For example:
Turn Greater Undead needs:

• a High Restoration Catalyst
• an Enigma of Repelling (think Repel Undead spell)
  

Conjure Storm Atronach needs:

• a High Conjuration Catalyst
• an Enigma of Daedra
  

It's not really complicated, just hard to explain concisely.

Why this mod exists

I've found it so boring for the progression of the mage to be self-centered. All this exciting looting that any other class would be able to partake in is just not relevant to the classic mage. Robes and spells are bought at a vendor, especially higher tier ones. There really was no reason for a mage to get out there outside of just killing shit.
There was also a game balance aspect kept in mind. Adept level spells like fireball are way way way too viable and cost-efficient, especially later in the playthrough. This is because expert level spells are just too expensive. So I've made them cheaper! Now they're pretty much as expensive as adept-level spells, making them downright superior to their less sophisticated counterparts.
The counterweight to that is this slightly complex item system I've introduced. The result is, pretty much, the Morrowloot-ification of spell tomes. Adept level spells are a small challenge to gain access to after getting the skills and tomes, but it's very doable as there's only one item to be found. Expert level spells are transformed into something more rare but more powerful, just like high grade equipment as found in Morrowloot! To get access to expert-level spells, you need three items instead of one, which is the spell tome, the high catalyst and the enigma. I've thoroughly playtested this mod and these items are just rare enough so that you'd get them at around the same point in time as to where you'd learn actual expert level spells in vanilla.

Technical stuff

This mod's effect are introduced via a perk automatically added to the player. This uses the same script as Skyrim Unleveled and will also show up in your mod organizer as a conflict or override. Fear not, this script is literally the same file and the mod order/install order between the two mods does not matter.
This perk is very simple. It applies a spell cost multiplier to the player (and the player only) that activates when the conditions as described above are met: if you lack the required items, you get a spell cost debuff. A significant one.
The enigmas make use of spell keywords assigned to spell magic effects. All expert destruction spells with the MagicDamageFire keyword, for example, will need a fire engima to be cast, as well as the high catalyst of the spell's school. This means that appropriately keyworded modded spells are fully compatible with this mod. Shoddily made spell mods will obviously not work. Keywords are important!

Credits

The models used for the catalysts were from bethesda. The ones used for the enigmas are from these modder's resources packs:
https://www.nexusmods.com/skyrim/mods/68755 Modder's Resource Pack - The Witcher Extension by Oaristys
https://www.nexusmods.com/skyrim/mods/16525/?tab=files Modder's Resource Pack by Oaristys and Tony67
Any minor texture edits are made by yours truly.