I have a '94 that is nearly the same as the '93 and it is very reliable. I don't know if the '93 has the same engine, but if it's physically in descent shape (no major issues with the chasses, transmission, electrical, etc.), then it might be worth putting some work into it. If you can do much of the work yourself (and you enjoy the work) then it could be a good "fixer-upper". Once it's running well I think you'll be pleased with it. For $600 they're basically giving it away. A working '93 would go for $1000 to $3000 depending on the condition (miles don't seem to make much difference). If you want to learn more about common Jeep issues, check out the first posting on this page ("Things to know about Grand Cherokees"):
http://www.automotiveforums.com/vbul...d.php?t=411199
I'd take it if I had time to fix it up. If you're intersted in it for winter, be sure to check all the safety stuff like the tread on tires. Also check the steering, brakes, etc. Factor known repairs into your total repair cost so you have an idea what you might end up paying overall.