I think this has been repowered with an M20B25 already and being an E21, probably 150kgs lighter than a 6cylinder E30, so power to weight ratio would similar to an E30 with an M52B28 if not a bit better.
These cars rust, you can fix them and then they will rust again.
I pretty sure I have seen this car in Christchurch and it wasn't pretty. This is a car that needs to be viewed and driven before bidding, unless you can get it for about 3k.
My guess is it will sell for 6K