Hammacher-Schlemmer, Home Shopping Network, Amazon and others have offered the Excalibur Motorized Pool Lounge, for $60 to $150 or so. It looks like your basic big ugly pool float; but in addition to the usual cup holder, it has two joysticks that control underwater propellers.
It may seem cool to be able to silently swoop and spiral around your backyard pool, but you better own an oil well -- or at least a battery factory -- if you're going to get one.
You can spend more money running it for an hour, than you spend to buy it. I received one as a gift about five years ago. I used it once.
The float uses 12 D cells (with no built-in charger); and a set of batteries will provide just a 15 minute cruise.
Alkaline D cells cost about a buck-fifty each. A full boatload will cost $18. That works out to $72 for an hour, plus sales tax.
If you want to emulate Gilligan's planned "three hour cruise," figure on spending close to $230 -- and you'll have to put Excalibur in dry dock every 15 minutes to change batteries.
Also, when you're onboard Excalibur, you're dry. You never touch the water, so why be in the pool? You may as well buy a boat, or stay in bed and save the money.
For comparison, a 80 horsepower outboard motor -- big enough for a 16-foot boat carrying six people -- will use about eight gallons of fuel per hour, costing about 16 bucks, much less than the cost of propelling the inflated motorized pillow with one aboard.