I'd pay 3k for a mint 16v quattro B3.
£1K for a mint base model B3
and £500 for any B4,

less for a coupe, I just don't like them.
I bought that 2.8q B4 a couple of years ago for £800, nicked the wheels off it and got £1500 for it, but it wasn't easy to sell, nobody wanted it.