It's not that being an asshole is initself appealing to girls (or at least not many), it's that assholes are better able to come across as disinterested. Girls like to think they are getting the better end of the deal if they date a guy - the want a guy who's better looking, a higher socail rank or richer and so on. So a guy who actually likes her and can't conceal his affection will come across as valuing her too highly, whereas the asshole won't value her anymore than countless other women and so she'll get with him thinking he's out of her league because he doesn't care what she thinks.
Imagine a second hand car sales man seems really eager to sell you a car, you'll be suspicious. That's how girls react to nice guys. If the salesman doesn't seem to care if you buy it your more likely to think he's got less to gain and so the deal is better for you. (Even though it probably isn't.)
Also rememember, there's nothing wrong with cheap dates, just don't let her know that.