Welcome to United Bimmer. The E30 is an excellent car to drive but with the average age of then around 25 years old they can have a few issues. They are great to learn on if that's what your interested in. However expect things to break and budget accordingly. If you have no tools or available resources to fix problems then maybe it's not the best option unless you have the money to pay for things as they pop up. I don't want to discourage you, as their are some E30's with overdone million miles!! On the original chassis and engine too. Try to find one in good shape with the maintenance records. You would really want to get one that you know has been maintained properly.
I've seen people find good E36's for as little as $600. The coolant system is the weak point on the car and for around $400 you can have everything replaced and good to go. Regardless of which model you choose their are lots of people who have tons of knowledge on both models.
I've owned my 98 E36 for 7 years and I still have the service records for everything I've bought both maintenance wise and aftermarket. I had my water pump, thermostat and clutch fan replaced out of nessecity due to overheating and other then regular maintenance (fluids, filters, spark plugs, etc) i haven't had to spend large amounts. They are no more expensive for regular maintenance then any other car. Just don't then over heat. Both the E30 and E36 engines don't like overheating