Increased the prices of certain Argosy items to make it harder to trade for items. Also a version which changes the items to be more useful (while still expensive). Updated for Sunbreak (old file can be used with base game). Sorry for lack of screenshots, I've not gotten far in the game. 

Increased prices:
Whetfish: 400 -> 500
Great Whetfish: 600 -> 800
Loc Lac Ore: 50-> 200
Bhernastone: 50 -> 200
All scrolls and other trade-in items have had their price doubled. Other item prices unchanged.

Enhanced Argosy Items version (keeps changes above as well):
Upped amount of Gloamgrass Buds you can buy at once from 5 to 10, and made them slightly more common. (rate: 40; numb: 10)Herbal Medicine-> Mega Potion; Unlock after 3 star village quests unlocked, or two star hub quests unlocked; cost 200; Normal StockNet-> Tranq Bomb; Unlock after 3 star village quests unlocked, or two star hub quests unlocked; cost 250; Normal StockGunpowder -> Demondrug; Unlock after 4 star village quests or 3 star hub quests unlocked; cost 400; Rare Find (Rate: 35%; Amount Purchasable: 5)Raw Meat -> Armorskin; Unlock after 4 star quests or 3 star hub quests unlocked; cost 400; Rare Find (Rate: 35%; Amount Purchasable: 5)
Poisoned Meat -> Dash Extract; Unlocked after 4 star village quests or 3 star hub quests unlocked; cost 500; Normal StockTinged Meat -> Demon Powder; Unlock after 5 star village quests and 3 star hub quests are both unlocked; cost 500; Rare Find (Rate: 30%; Amount Purchasable: 10)Drugged Meat -> Hardshell Powder; Unlocked after 5 star  village quests and 3 star hub quests are both unlocked; cost 500; Rare Find  (Rate: 30%; Amount Purchasable: 10)Poison Smoke Bomb -> Dust of Life; Unlock after High Rank unlocked; cost 800; Rare Find (Rate: 40%; Amount Purchasable: 5)Sonic Bomb-> Mega Demondrug; Unlock after High Rank unlocked; cost 800; Rare Find (Rate: 25%; Amount Purchasable: 5)Flash Bomb-> Mega Armorskin; Unlock after High Rank unlocked; cost 800; Rare Find (Rate: 25%; Amount Purchasable: 5)[Open slot] -> Max Potion; Unlock after High Rank unlocked; cost 800; Rare Find (Rate: 40%; Amount Purchasable: 5)[Open slot] -> Ancient Potion; Unlock after High Rank unlocked; cost 1000; Rare Find (Rate: 15%; Amount Purchasable: 5)

Compatibility:
It will conflict with other mods that edit the ExchangeItemUserData.user.2 file (file path: natives/STM/data/Facility/TradeCenter); either this mod will overwrite/revert changes of the other, or the other mod will do the same to this one. Changes of one mod will have to manually be added to the other's edited file. Anyone is free to add my changes to their mod file and upload it for compatibility, if they so wish. 

Mod suggestions:
Use Rewards Multiplier with a decimal value (eg, 0.5 for half rewards) for Kamura points to make it even harder. 

My other mods:
Weaker Palico and Palamute Weapons
Increased Item Prices
Decreased Monster Rewards

Unfortunately, it looks like I can't add any more item slots than what's already there with MHR-Editor (there were some unused slots, which allowed me to simply add items rather than replace).

Permissions:
Don't sell it or put it behind a paywall. Otherwise, do as you wish with it.