I believe the jetski rental place behind Zylas in the channel has 1/2 day and full day special pricing. Not positive on prices but think its fair to estimate $400-$500 for a full day per machine. There is also a place on Rte 3 just south of Jays Marina that rents jetskis on a long term basis and will deliver them to your location. Maybe someone out there has the name, I don't off hand.
As far as tips....check out the State's website for Marine rules. And if you fall within the dates that require boater certification the rental place should require you to produce your card or you can take a short version of the test for a temp (14 days-one time only) certificate. First and foremost become one with the 150' rule, the no-wake rule and the Right of Way rule. These are the three fastest ways to piss off other boaters. Secondly, have fun...
safely.