I probably wouldn't buy it for the repairs noted.
If an ATV is in good shape, here's how I figure its value.
Start with the price it could have been bought for new at the time it was originally made.
Deduct $1.00 per mile.
Deduct $100 per year.
That will normally get you really close to fair market value.
If it's not in good shape, deduct for damages or service needed. Personally, I don't buy an ATV that's been beat up. There's too many clean ones out there to buy something that's been abused.
EDIT TO ADD: I haven't had to put $1,600 into repairs in the last 7 ATV's I've owned combined