Like ChicoRaton, I'd also get a Betta. Extremely beautiful, not very aggressive by himself, but not a lot of fish are if they are alone. If they are overly aggressive, chances are, you couldn't put it in a 10 gallon anyways. If you want an expensive fish, there are lots of specially bred Bettas, like Halfmoons, Butterfly, etc, that cost quite a bit. Look for a local breeder for a nice strain. Or you can check out some reputable online Betta breeders if you want to go that route.