You need to know, what you are getting into.
Just because he says the sails are good doesn't mean anything, you'll need to lay them out look for tears, dirt, mold, etc. Even used sails could be over $500and much more for that boat.
Does it have cushions.? While it doesn't hurt the sailing properties it can be well over a $1,000 just to do it on the cheap.
A small 2 stroke OB could be $500, if you're lucky.
Make sure it has a tiller or rudder.
If indeed the standing rigging is bad, that's not cheap and could add up quickly and you can't cheap out on that, it's holding your mast up.
Do the winches work, are they there..?? Price those babies out
Do some research about checking for soft spots in the hull, deck, etc.... Look in the bilge se if there's any water, it may help to see if there are leaking windows, deck hardware, etc.
Make sure you know if you need a title for the boat, the trailer or both to register them in your state...
You don't want a $700 anchor.