An '86 could be anywhere from -500.00 to +$10K Here are two extreme examples I have seen:
Seized rusted up engine, hole busted through hull, crushed windshield, sat at the bottom of a lake after sinking, uph. missing & damaged, no trailer...I bid $600 for Ins. Co. to pay me to take the boat & cut it up for disposal, was outbid, they paid the low bidder $500 to do the same...
Pristine 1985 with documented properly replaced floor, carpet, 400hr engine that was detailed & running strong, new cables, new wiring, new OEM quality interior, rebuilt trailer, clean exterior was asking $11,500, sold for $10K (no stereo no bimini)
Thoughts on used ski boats: The best used ski boats always come from promo owners, they are compensated to maintain their boats in showroom condition. The problem with this is they will almost always be no more than 2 years old, and are currently bringing $45K+ These boats are virtually a requirement to have IF you are chasing 3 event tournaments and want to be competitive. Most recreation skiers who want a quality ski pull will be perfectly fine behind '80s & '90s technology, what you want is a dependable towboat that is ready to go every weekend.
I recommend lower priced fixer-uppers only for the buyer who has the time, energy, facility, tools, and mechanical aptitude who can go through the boat/trailer and make repairs as they go as needed.
For those outside the above description: pay more but be sure you are getting more, demand documentation, receipts etc. for work done. This is common in the car world.
Good Luck!