Um .... er ... gosh. Well, let's see....
Do you want a Porsche-purists opnion or a "Bling" opinion?
Depending on what they've done mechanically to the ... uh, 911-sorta-thing ... it started out as a 911SC, if it's an '81. SC's are priced a bit less than 18K unless they've been thoroughly "worked-over" ... in a
restorative manner. 911SC's can go for $10,500 to around $15K depending on condition and maintenance. You can occasionally find a great deal on an SC for under $10K, but it might need a little something re-done.
What kind of car are you looking for? I know of an '88 Carrera that would go for less than 18K, and is really a beautiful car.
That's where I'm comin' from. I own and '83 911SC.
(Sorry, but this one looks more like an Acura.)http://sandiego.craigslist.org/nsd/cto/1200971479.html
Hope that's a start.
DC