First off never get truck fuel, they price is instantly $2+. Always get self serve, I have found that most of the time at reasonable prices around $1.79/gal.
If you are a member of AOPA and charge it to the AOPA card you can get a 5% rebate.
Oh if you are in South Florida, the cheapest place that I have found is the airport at the Big O, $1.75 for self serve, and you don't have to spend 45 mins on the ground trying to get it.
At worst, you screw up and die.