The ski will have no trouble pulling a tube. The price sounds about right, maybe a little high, if it's in really good shape and includes a trailer. Around here it would be $1500 to 1600, so I'm thinking this is what the seller will take.
Let us know if you need any help about what to look for when purchasing a SeaDoo.
BTW, it's not easy pulling a tube or anything else behind a PWC. The law requires you to have a driver and an observer when pulling a tube, skier, etc. Which means you will need to carry three people plus the tube.
Lou