I'd say it's definitely worth fixing, regardless of if you decide to sell it or keep it. If you get rid of the jeep as is, you wont get much for it. Maybe $1,500-2,000. Fixed and running properly you could easily get twice that.
Parts to do a head gasket job really aren't that expensive (as long as you didn't trash the heads), it's the labor that makes the job so expensive. And doing the work yourself really isn't all that difficult - just time consuming. And since you're going to get rid of it anyway - what's the harm trying to tackle it yourself?
The real question however, is what caused your HG to fail? Sometimes it's a minor problem, like you ran out of coolant. Sometimes it's a major problem. I'd try to track down the cause of the failure before you spent any money on anything. Also, make sure you check for warping and cracks. Not sure if heads in the KJ's are aluminum or not - if they are, they can easily warp. Also have known of blocks that have cracked and/or needed machine work, but those are extreme cases. Just be aware...
I helped a buddy replace head gaskets on a '97 Ranger V6 (basically the same process) and it was really wasn't all that difficult, and you only need basic hand tools. Took us about 6 hours, and that included time to chase parts and tools down, and to figure out what we were doing (did it without a manual - I don't recommend it, lol).
