need suggestion on AC problem...

Hey guys.... took my car in today bc my AC was not working... I found out I have numerous leaks in about 6 different places. It was previously recharged and in about 5 months it leaked over 2 lbs of freon. For now i just had it recharged with another 2 lbs... $150. To fix the all the leaks would probaly cost about $1000. They can't tell which leak is worse. I was planning on keeping my car through college(another 4 years) and if it leaks the freon out every 5 months then i will be spending about $1200 while the leaks only get worse.
It is a 1990 LS coupe. So far i've put about $400 into the car as far as fixing little stuff and tweaking it. I bought it for $3500. Should I keep refilling it, fix it, or sell it? Also the ABS has some kind of leak in it and it keeps on having to pump up so that might go bad as well. Sry... I'm just kinda upset about it and I don't know what to do. My main concern is cost. I checked the kelly blue book value and it is about $4500. If I could sell it for that then I would pretty much break even and maybe get another car... I don't know... Has anybody had this problem? Thanks for all of your help.