I will chime in here. One of my favorite cars I have ever owned was the Bentley Brooklands that cost $23,000. So much car for so little money.
In the $15,000 range you can get a nice Rolls-Royce Silver Shadow. The cars are amazing, and the club is top notch with tons of events. The Rolls club people really get out and use their cars for tours and rallies. It is not the snobby group you might think it would be.
For only $10,000 you can get a BMW 2800 or 3.0 CS/CSI. A beautiful and reliable car that eventually has to be worth considerably more than that.
The other BMW coupe, the 633/635csi is also a nice inexpensive classic for only about $5,000 for a very nice example.
My pick if you can swing it would be the Silver Shadow if you like Rolls-Royce cars. There really is no car with that much curb appeal for so little money.