Not sure about the ones on Ebay, but my father bought an 80cc from BJ's a year ago. It looks very similar to the Suzuki LT80. Paid about $1000. He figured he'd have it around so my kids would want to go see old "Papa Daddy" more often. As my boys got better at riding and more aggressive, this thing started falling apart more and more.
I guess if your kids will use it to just putt around, might not be a bad idea. If they will ride it like I think they might, you might want to go ahead and spend the big bucks. Check traderonline.com and go to cycle trader. You'll probably find a better deal and a better dealer. Good Luck