Penny, mine is an '89. I have done several structural upgrades to it, and I have no idea what I would price it at. Which really doesn't help you at all, does it? IF it doesn't need any work, then the price might be okay. Unless they added it, the '89 does not have a grey water tank but is plumbed (or mine is, at least) so that a blue tote tank can be used. Unless it has been raised, the ground clearance on it will be rather low. This may or not be an issue for you.
There are some pluses as well as minuses to them, but I have to tell you that I absolutely adore my '89. Those that know me are tired of hearing about me looking at new trailers. I'd love to have a new one, but I just can't seem to part with mine and I have yet to find one that I like better.
IF it's in really good shape (inside and out) then I think that $3500 would be an good price. IF you love it and $4,000 is in your budget and it's had no modifications to it, then I'd say okay. Remember, though, at that age, you may have some cash outlay and need to do some repairs. That's just a fact of life.
If I were to list my '89 today, I'm sure I would list it for more than what they are asking. However, I did put on a new axel, 14" tires
, reinforced the frame, raised it, added a welded spare rack to the front, AGM battery
, upgraded the converter with charge wizard, and other things. I'll never get my money out of it, but I don't regret spending it either.
Without looking at it, I really can't say, but I hope this might help as a guideline.