It kinda depends what you mean by maxed. Mostly mods. If you mean vanilla maxed, no mods, then surely you can max it for $500, maybe even a bit less. But with all kinds of heavy mods like Qarl's texture pack, FCOM, and RAEVWD (LOD replacer), the game can get pretty strenuous. I build my current computer for a little over $500 and I can run plenty of mods to make me happy. I'm not getting 60fps everywhere, or anywhere (stutter remover caps it at 30), but it's certainly playable and highly enjoyable.