Same as any older boat the most important thing is the motor, check compression and check lower unit fluid, as well as making sure she's pumping a solid stream of water. Unless the boat was run onto a pier that hull should still be solid.
$3000 doesn't seem too bad if the motor runs well. I can't say for sure but being a 1989 you're probably going to have to throw some money into it day one to get it where you want it. Hopefully that Gel can still be saved, clean it good with some degreaser and then hit it with a wool buffing pad and some course compound and hopefully you can get some shine back into her.
I scooped up a 1989 360V about a month ago for $2500 and had to put about $600 into it before I even took it on the water between new steering cables, new battery, new trailer bunks and carpet and a used 24v trolling motor. The gel cleaned up surprisingly well with a decent buff to put some shine on it for the rest of this year before I do it more thorough this winter.
Just really try to look over the boat hard before you pull the trigger on buying it, I was dumb and forgot to check the steering and didn't notice the throttle cable on the hotfoot was bad either. Overall love the boat though, and since it's already a 1989 you don't really have to worry about it depreciating in value too much, as long as the motor still runs well you should be able to get that $3000 back in a few years if not more if you work on it.