Spoon -
The water trampoline was very close to shore (this is Great Bay I am speaking of), but the water depth dropped off very quickly. The trampoline was probably about 20 feet from shore, but dropped to over my head (6 feet) at about the same spot. I could walk out to it, until the drop off. This way you could slide into the water and not hit bottom. I had to stay with my DS6, who is not a strong solo swimmer. They usually charge $5.00 per wrist band (that shows you paid to use).
The jet skis were $40.00/half hour
2 chairs with umbrella - $10.00 (included one free drink, but they would continue to ask if you would like another and would bring them out to you for the cost.)
Trampoline $5.00 per person (not sure if it is kids only)
I bargained with the guy and got the chairs, jet ski and umbrella for $45.00. Thought it was a good deal.
Not sure what you mean by rent one per family - if it is jet ski, I could have come in and let my DW use it if I wanted to, but she didn't want to do that. So DS6 and I used it for the whole time. It was so much fun. There is also a shipwreck out on the rocks to the right of the bay as you are looking out from shore. We went over and checked that out. They don't let you go near the ships, but we did see some people on the regatta excursions and stuff. It was a lot of fun.