Umm... that is BS. When a company makes a mistake, and expects you to foot a $600 bill, that could be illegal (check your state's laws on business practices). They should foot something like that, and if they continue to refuse, mention legal action.

They sent you an inferior product, which isn't even comprable to what you ordered. That would piss me off to all hell. Try being nice (For as long as possible... this really does matter), but if they continue to be bitches, make it known that you will be a trouble customer and that you know you will win.