Not all striped raphael catfish are the same species. The usual species is the black and white Platydoras armatulus but sometimes other species, such as the chocolate brown and white Acanthodoras cataphractus get imported instead. Yet another contaminant is Orinocodoras eigenmanni, a black and cream coloured species.
Another species, Platydoras costatus, is often quoted as being traded in aquarium books and magazines, but apparently isn't traded, and the name has been used in error.
They're all much of a muchness in terms of size (15-20 cm), behaviour (gregarious rather than solitary), and compatibility (good with anything too big to swallow). So telling them apart doesn't matter all that much. In the UK at least, the price varies but tends to be rather low, typically £5-10, depending on the size of the specimen.
Cheers, Neale