I owned a 1978 928 for a couple years, everything is expensive! Go price some parts at a dealer or at the cheapest place I found for OEM, used, and aftermarket parts
http://www.928intl.com/ If you own this car, you can't JUST like being under the hood, you have to have the money to buy the parts too. The Civic or the WRX don't even compare to the 928 in upkeep price, but you get what you pay for. My 1978 was comparatively under powered at 225 hp, but the handeling was beautiful. I could actually steer the rear end with the accelerator by changing torque to the wheels during a turn (I don't mean power slide either).