I think there was a thread somewhere discussing Band of Misfits at different prices, and I think it works at several different price points ($4, $6, maybe $7).
I think Rats would be quite interesting at other prices. I've sometimes wondered what it would be like if the top five Rats cost $4, then the next five cost $5, then $6, then $7, or something like that. But other prices are interesting for Rats even if they're uniform. I'm guessing Rats is strongest at $4. At $5 there's too much opportunity cost in passing up other $5's, with not many TfB cards hitting $5 much harder than $4. But then at $6, I can imagine them being maybe more viable, since they are close enough to $8 that a lot of TfB cards can bump you up to Province (Remodel, Farmland, Butcher). At $7 you're close enough to be able to Upgrade or Remake them into Provinces. At $3 they should be much worse than at $4, since you usually only buy one Rats anyway, and the price difference between $3 and $4 is not that great.