1. Every used car is a pig in a poke
2. Things happen

That said, I have had a base coupe and an SRT roadster and beat the snot out of both of them commuting 500+ miles a week. My biggest expenses have been tires and windshields (5). Be prepared to spend money on maintenance and tires -- especially tires. If the tires on the car you want to buy are new, have the suspension checked or you may be sad. If not new tires, check the wear pattern. If the car is lowered, you must check the suspension to ensure a proper alignment can be performed. Replace the steering damper if it is not new (cheap and oh, so worth it). Considering 1 and 2 above, figure $200/month for maintenance and repairs averaged out over time. That is barring any unpredictable catastrophic failure.

Do you know the car's maintenance history? Are you buying from a reputable dealer, consignment lot or private party?