Air Suspension Light On; Bumpy; Rear is Lower Than Front

My 1995 lincoln town car is very old, and I'm trying to ride it out until I graduate in 4 weeks and drive home from VA to NJ. It has had many problems, but we've always gotten them fixed, or at least put temporary fixes on them ( the car has 260,000 miles on it, but runs very well). Anyways, I was driving down a relatively flat road today (not too fast - 45 mph), and I noticed it started acting weird - super bumpy. At first I thought it was a flat tire, but that wasn't it. I was almost to work, so I decided to wait until I got there before I pulled over to look at it. When I was a couple miles away, the " check air suspension " light came on. When I checked the car out when I got to work, the rear of the car was much lower than the back. I would love any information about what could be wrong, how much it will cost, what damage it could do if not fixed, and all those things before I go to a mechanic in town. I'm a broke college kid with limited automobile knowledge and I really don't want to get taken advantage of, sadly. Especially if I don't plan on using the car that much longer. Any information would be greatly appreciated. Thank you so much!