Life long boater and experienced shade tree mercruiser mechanic, Don't have a ton of experince with skis but will share my experince-
about 7 years ago by dad bought a 2004 Sea doo gti rfi le so I could teach my kids to water ski in shallower water. It had 100 hrs on it and I think he paid $4k with a trailer. It's a two cycle 110 hp. And really has been nothing but a ton of fun for us. No real maintenance issues, yeah the synthetic 2 cycle oil hurts at $50 a gallon, but I buy one a year. I do the winterization and change the pump oil annually (which is a bit of a pain). At 175 hrs i resealed the jet pump and replaced the wear ring, plus one RAVE valve rebuild. Only issue I've had is it fouls the plugs a bit, I think the throttle position sensor needs to be reset. While not a great solution I just change the plugs after a couple weeks, two of them is less than $5...
Bottom line it was a well cared for ski, unless you're right on the water people stop using them because life is too busy. If you find one like this it's worth paying a little more for one a bit newer, but I'd stick with a mid to lower end ski. It does 50 ish and unless the water is like glass it's a crappy ride, my kids have skied, wakeboarded, and tubed behind it.
Good luck