You spend less money on upgrading your entire house, cellar included, than the 230,000 gold Robin and Pierre ask for these tables, and as someone who doesn't prioritize money I've only ever managed to get them once. It shouldn't cost a quarter of a million gold just to decorate my house, and after looking online for a mod that would decrease the price of them, I came up blank. So I made it myself.

This simple mod allows you to alter the price of the Furniture Catalogue and Wallpaper Catalogue to anything you want. Want them to cost 1,000,000 gold each? Don't know why you'd want that, but go for it. 2 gold for both? Easily done.

Instillation and Usage:

 1. Install the latest version of SMAPI.
 2. Install Content Patcher.
 3. Download this mod and unzip it into Stardew Valley/Mods.
 4. Run the game using SMAPI. Upon loading a game a new config.json file should appear in the Furniture and Wallpaper Catalogue Reprice folder.
 5. Close the game.
 6. Open the Furniture and Wallpaper Catalogue Reprice folder you put into your Mods folder.
 7. Open the new config.json file. You'll see two fields: one called FurniturePrice : 200000 and one called WallpaperPrice : 30000. Those numbers are the default price of each table. Change them to anything you want.
 8. Save and exit the config.json file.
 9. Done! Your new prices should be set when you load back into the game.

Uninstallation:

 1. Remove the Furniture and Wallpaper Catalogue Reprice folder from your mods folder.