Jimbo,
I have a fairly unique outlook on Gas for Boating.
Of all the costs associated in boating Gas is but one cost of many, yes its an expensive hobby. Right now, Gas is roughly a buck more per gallon than last year, this makes each fillup cost roughly an extra $150-180 Bucks, My boat has twin 100 Gallon tanks (I don't let the tanks go below 1/4). With Both Tanks full it will take about a month to 5 weeks till I need to fill up, unless we take a trip. I work at home, I don't even put 6000 miles per year on my vehicle. So in a month to 5 weeks the average commuter will put almost as much gas in their car as I do in my Boat and Vehicle.
If you don't have the money for the gas then you really shouldn't have a boat.
I spend vastly more money on my Accelerated Boat Loan, Dock Fees, Maintenance, Registration Fees, Customs Fees etc.., than on the Fuel.
If your interested, My Boat is a Cruisers Yachts 3375, Its LOA (Length OverAll) including Extended swim Platform is 36 Feet, with a 11 foot 9 Inch Beam. She has almost all of the extras, Remote Spotlight, Radar, GPS Chartplotter, Reverse Cycle Air/Heat, Windlass, Vac-u-Flush Head, Dual Refrigerators, etc. The Only item on my Wish List would be a Generator, even so I wouldn't use it much. She's Powered by Twin 7.4 (454) Big Block's mated to V Drive Inboard transmissions With Closed Cooling System. Her Best Cruise speed is about 28-30 MPH burning about 28 Gallons per hour, which means she gets at best 1 MPG. Her name is "TARDIS" if you are a Science Fiction Fan you should know what it means.
Just got back from Sodus Bay on Lake Ontario, what a GREAT DAY.
John