I would say that is a little pricey for a 633
there is the 633, 635, L6, M635, and M6 (in the US)
the latter of the three are worth the most...
I would say a good low mileage clean example of a 633, no rust all original would be worth @ 2k - 3k tops
those are the wrong wheels on that one =) the paint is pretty shiny...is it original? or did someone do a half ass repaint...all stuff that will hurt you down the line. How many miles are on it? Do all the electronics work?
These cars are not cheap to repair...the parts are not horribly expensive however if you like to work on your car yourself. I would not recommend an e24 to someone who cannot work on their own car or anyone who cannot afford 100/hour labor rates.