Edit: I fixed a screwup.
Oh, so let's say you do that every day. How long is the payoff.
Year 1 $5,000/365 = $13.7/gallon
Year 2 $5,000/730 = $6.8/gallon
Year 3 $5,000/1095 = $4.5/gallon
Year 4 $5,000/1460 = $3.4/gallon
Year 5 $5,000/1825 = $2.7/gallon
Year 6 $5,000/2190 = $2.2/gallon
Year 7 $5,000/2555 = $1.9/gallon
Year 8 $5,000/2920 = $1.7/gallon
Year 9 $5,000/3285 = $1.5/gallon
Year 10 $5,000/3650 = $1.36/gallon
Got to today's gas prices in my area by year 4. That's actually not that bad of a break-even time.