Build in buffer
On the off chance that you dont know spur of the moment whether the typical print of such a card is Uncommon or Holo Interesting, the best way to find out is to look into the card in a data set like the TCGplayer commercial center or pkmncards.com
They effectively double the mana rebate from Prosper, greatly improve the Treasure synergies in the deck, and also work beautifully with some of your new win conditions Win Conditions Im certain Prosper didnt sign a deal with a demon without knowing that they could stand to well, prosper from it
If you can realistically expect to trigger your draw-2 effects at least once per turn cycle, you'll be floating a ton of extra lands into play, and your hand's already likely to be stocked given the archetype, so you shouldn't be running out of land drops any time soon
3 Trainer, which are nearly as rare and valuable
I've also seen people just toss in commons and think it's budget when many commons are more expensive than bulk rares
