5-800 would be going rate for a ski like this last I was looking (without a trailer), not because of condition but because you can't get many new parts anymore, that and stand ups are a dime a dozen as they are not as desireable. Though used parts you may be able to find if you know where to look.
Looks like a good deal in here, but IMO when you set the idle so it stalls instead of fixing a 5.00 kill switch I worry what else may be rigged, could it be adjusted when looked at where it will not stall and idle nice? I would believe 650 to be a more fair deal, sight unseen anyway.
If I didnt have my wave runner I was trying to get running so I could sell It, I would consider this, but not for 1k IMO