The car will likely be expensive to maintain - that is only my humble opinion. The shocks are expensive ($90 each + labor), the front end is expensive ($300 control arms + labor) and your water pump may be failing (plastic impeller $100 + labor). The brakes should be easy to fix (fluid and pads maybe rotors). Hopefully your battery terminals are just crappy - clean them and get the system looked at by Autozone? They check for free if I recall.
Not to discourage you (the 525 is ball when it works well and has been maintained), but you are looking at either becoming (hopefully you are?) a good mechanic or paying for one. Parts are still going to require your cash. And as pointed out, ANY 15 year old car is going to need maintenance. The E34 is a complicated beast and this board can help you tremendously, but never expect a 15 yr BMW to be like a Honda or Toyota (which is good and bad)
Good luck,
Scott
1995 BMW 525i w/139K miles, EAT Chip - (Gone)
07 525i 22K, 07 328xi (41K)
1982 Mazda RX-7 w/147K miles (Back again!)