I bought my 1989 E34 535i 18mths ago for $9900. Its a five speed manual with 195000 miles on the clock, 18 inch mags and full leather with sports kit. Its a fantastic car. I'll be selling next year and going to an E36 M3 evo as I will not need the bigger car then.
If your looking for a 535i, there is normally a few around in manual, shouldn't have to pay more than $10 unless its mint. Parts are easy to find on Trade me and wreakers.
E30 - Great cars unless your 2 mtrs tall like me, had a 325i, which was cool but cramp.
E36 - My wife has a 96 328i touring which is also a great car.
7's - Don't know much but I wouldn't want to pay the gas bill or park them in town.
Good luck and be patient!