www.iFourWinns.com

Some stand alone fuel flow systems are available, and the prices are as you quoted. These fuel flow systems will read gallons per hour and may keep track of how much fuel has been used. I know you said you are not looking for one that connects to a chart plotter. One limitation with the stand alone system is that it cannot give an accurate "Miles per Gallon" read out with out a GPS or other means to accurately measure distance. The Lowrance fuel flow I added was approx $170. If you consider the additional cost for a stand alone system, would the cost difference make a chartplotter worth considering? The Ipad or cell phone may also limited to position based on cell phone signal. My fuel flow gives me real-time gph and mpg read outs, and I can use the chartplotter menu to see how much fuel has been used since refueling, and even a season total. The chart plotter may even give you a total distance traveled per trip or for the season. I found that I definitely gain efficiency by trimming the drive up some. This might 5 - 10%, or maybe a bit more. Too much trim usually means the boat starts to porpoise.

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Surface Interval: A scuba diving term for that time between dives to relax and prepare for life's next great adventure.

Current boat: '02 FW 268 Vista
Previous boat: '95 FW 190 Horizon

How about this one?
http://www.defender.com/product3.jsp?name=us-marine-flow-totalizer-and-flow-rate-meter-kit-fuel-gas-engine&path=-1|311|2349076|2349081&id=2913294

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"Knot Easy" 2000 Horizon 240 Volvo 5.7GS /SX
tow: 2017 Honda PILOT EXL-AWD
prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
'68 Aluminum Jon Boat, 3hp Sears
'64 Water Wings