E28s
Great cars, the E28s. I'm on my third. There are a fair number of E28 owners on this board.
If you're hooked
, I'd get a good iS that someone else has tastefully modded (suspension and brakes) and maintained well, i.e. paperwork, but also expect to apply the "$2K rule" to bring it up to par. If you want more power, throw a E36 M3 motor at it or turbo the existing M30. You'd be into it for ~$10-12K and have a great car.
The Dinan Turbo, if we are talking the same car, was posted by BimmerBros whose rep has been discussed on this board previously (I bought my latest 5er from them). If you really want a Turbo, go with a TCD or Miller Turbo package and add it on to a stock M30. The E28 Dinan turbo approach is a bit dated and, as mentioned, parts would be challenging. Check out the Forced Induction section of the Mye28 forum for more M30 Turbo info.
Either way, you'd be into it for 1/2 of the Dinan or 1/3 of the Hartge, which is beautiful BTW but I'd be almost scared to drive it for that price.
And I admit it - I don't get the collector car value thing. Depends what you are into I guess. I like to drive, not clean.
Good luck!