basically there are a lot of different types of clarinets. there's the really, really common one that everyone thinks of when you say "clarinet," that's the B flat clarinet.

an alto clarinet i think is in E flat? it kind of looks like a saxophone (well, alto sax to be technical :P). it is kind of an unusual clarinet, i have to admit i have only seen it once or twice in person and never really heard it used in ensembles, so it's kind of a niche thing.

rayburn does have used instruments of varying levels of quality -- from basic student to pro. as with most clarinets, the cheapy cheap ones are like a couple hundred but they can go up to several thousand on the higher-end.