I'll give you some input. Based in my recent frustrations with my XJ (that you are aware of) I have been scouring Craigslist (So Cal) for the few weeks for possible replacements.
- seemingly clean late model 4.0/4x4 offerings, I would consider reliable daily drivers are listed by owner AND dealers rarely above $6k. These I would expect to be end user older used cars/buy and drive (actually a pretty good choice for that use other than MPG)
There are PLENTY of seemingly good buys early and late model that have "some issues" that may not be a big deal to someone familiar with XJ's but could scare a typical used car buyer. These tend to range in the $1k - $3k offerings
Then you have what most typical used car buyers might consider a beater, but someone familiar witH XJ's might view as a diamond in the ruff. These are commonly available at $1,500 and way below. (Sounds like the one you are looking at fits about in this category, but see below)
I bought my 1988 five years ago for $650. Aside from my desired upgrades and my recent issues, it really never really needed anything serious.
One thing of common value is the 4.0 engine and 4WD. 2WD models seem to take a big hit in resale. When looking at wranglers, the 4 cyl engines seem to take a huge hit in resale as well.
Obviously one of the biggest value points with the XJ,s beyond the classic platform is the 4.0, 4wd and solid Tranny/t-case inclusions. There are millions of 4.0/4wd/231 jeeps out there and the aftermarket options are crazy.
I have seen listings for early model (1988-1990) 4.0/4wd XJ's in the $1,500-$3,000 range. These are listed as buy and drives in various condition NOT "needs repair".
The one you are looking at has a clean body/interior (a big plus) but has a unique and much less desirable engine/tranny combo. (Based only on my review of listings). While this might be of interest to a die hard XJ enthusiast, from what I gather there is no added value for these unique attributes. If you are specifically looking for an early model 4 cyl. XJ then you are a unique buyer.
For the rest of the market, the seller should be aware of he fact they have a very undesirable model on their hands that does not posses the desire able attributes of the typical early model XJ.
All that being said, given the likely work needed, the engine selection and the model year I don't see this particular XJ being worth more than a few hundred bucks. Certainly NOT approaching $1k
Bottom line is your getting a clean interior and exterior and to realize any significant value, your probably looking at major/difficult repairs or a 4.0 swap.
If your into older, unique XJ variants, go for it. If your looking for the best value in an early mode XJ, search around you will find plenty of late 80's/early 90's 4.0 4wd in good condition in the $2k -$5k range. And some really clean later model XJ's in the $3k to $6k range.
To answer your question, I would figure an offer in the $500 range. If you love it and know you can get it running, maybe go $800-$1k. After that it becomes a personal "I want it" decision.