Less than $100 for a new phone with more storage (memory is RAM, which isn't your problem) is almost impossible. For a used phone, check
Swappa.
Straight Talk uses all 4 carriers so any phone is compatible with it - but the question is which carrier gives solid coverage every place you need coverage? That's the one you go with. (Straight Talk is a virtual network operator, not a carrier.)
(It's possible - but rare - to find a good buy on Ebay. It's usually not possible to find one on Craig's List. And you need someone local, so that Verizon - if that's whom you choose, and where you'll meet to buy the phone - can verify that the phone is acceptable for [and usable on] Straight Talk. Not all Verizon phones are - and if you want Verizon, it has to be a Verizon phone.)