I imagine for an oil change alone at an independent you are looking at $150-200. Sorry. Oil aint cheap and most shop rates are $100/hr around here. You could try one of the Curry's locations (I've used the Chantilly one, but they are also in Dulles and Falls Church). They did do some basic work (in fact, it may have been an oilchange) and some tire mounting for me. When I had a major issue, they realized it was beyond their skills so I went to IMA. A firend of mine had a disasterous experience at their Dulles location with his 996. You have been warned
RPM in newington is another shop.
If you haven't already, there is
www.dorkiphus.net DC area group of Porsche fans. Mostly 911 guys who like to "DIY" because of high shop rates. Several of us have or have had boxsters too.