Ask yourself the question, "Am I buying this because it's a good deal or buying it because I need a platform to build on"? Also, you already have a TJ, so do you really want/need another? I went through a similar thing recently, where I bought a TJ cheap, spent a bunch of money on it, and planned to wheel it. In the end I didn't use it that much and it sat around. Ultimately, I ended up selling it and staying focused on my LJ. As much as I like the TJ/LJ platform, having one is enough for me. Both time and money are limiting factors, with time being the most precious.
That said, if you're really needing one to build, if it's a rust free body and frame, minus the doors and top, I'd say no more than $1800. On the plus side, given the 4 cyl, you're already geared better.