Most enjoyment per dollar: I want to say RimWorld, but that shit’s expensive at over a hundred dollars for the base game plus expansions even during the rare times it's on sale.

So I'd have to say Terraria, which I bought for maybe fifteen bucks back at release when it had like three bosses and IIRC ended at Skeletron. Fifteen years of massive free content updates later, it's a sprawling randomly generated Metroidvania with dozens of bosses and an endgame that barely resembles its beginning, and I've probably done a dozen full playthroughs over the years.

That's not even getting into the mods, with tModLoader being given the official seal of approval and letting you swap between a multitude of content overhauls from within the game itself.

Least enjoyment per dollar would probably be Caves of Qud. It's not a bad game, but I went in with sky-high expectations that it couldn't possibly meet and I couldn't bring myself to enjoy it for what it was; instead feeling frustrated at what it wasn't (and didn't try to be). It didn't help that I regularly play freeform games like CDDA and Dwarf Fortress and the comparatively static structure of CoQ felt extremely restrictive in comparison.