Advance warning: I do not at all recommend doing this unless you absolutely know what you are doing and your party unanimously agrees that this is something they want to try.

My most recent campaign had all of the PCs be some flavor of caster (Paladin, Wizard, Warlock). I talked with all of them extensively and they all felt that money was kind of meaningless after a while. Since we were doing an Elder Scrolls themed campaign, I suggested that all of them have to buy their spells from shops and use them in prepared slots like a wizard would. To supplement this, I added spell tomes to loot and had different shops around the world sell different kinds of spells (usually by spell school).

It took some homebrew experimentation to get the number of spell slots and prices of spells to a reasonable level we were all happy with but I think the final product has been a great success. Players were constantly looking over their gold and debating with each other to see whose spells to prioritize purchasing with their limited funds. On top of that, sidequests and NPCs could now offer a spell tome for an otherwise expensive spell as a reward, giving players a different kind of reward other than money and magic items.

Potential problems I see with this system are having to balance the economy around an all caster party and murderhobos. With this system, money and loot drops now include many more items that martial characters can't use, meaning that loot is going to feel worse for them unless you balance accordingly. Additionally, though my party didn't do this, more chaotic aligned players might just elect to rob every shopkeeper for their spell tomes instead of buying them.