Well, the reason the oil change is cheaper is because they probably use low quality oil and filters and BMW charges out the butt for labor. But the E36 is actually the easiest oil change I've ever done. So you should really just do it yourself. I know you don't want to but it's the best, and cheapest way. Just see if any of your friends could help you out with tools.
You need is a jack (two is better so you can get the car level.)
A jack stand.
7 Quarts of 5w-30 The car holds 6.3 Quarts)
An oil filter.
A funnel. (you can make one out of a coke bottle.)
A 17mm wrench for the oil drain plug (I think. Might be 16.)
and a 12 or 13mm for the oil filter bolt thing.