Minimum for me is double the initial offering pay. But that doesn't apply to all of the gas stations, just the ones that I do the most. I expect a little more from BP because they are harder to get and difficult to do in a route because they are so spread out. I did a lot of Shell stations last quarter at a lot lower pay than I normally would have because someone was gobbling them up and I really needed to work.
I will do the simple ones like marathon and citgo for as little as $15 each, but there has to be a route that will make me enough money to put in the work. I have offered to do marathon and citgo routes, only to have the scheduler gut the route and offer me a bunch of spread out stations that won't cover the cost of driving away from the house, let alone the cost of driving between the stations.
Plus I have to take into account for the limitations of my knees. The stations that require more effort and more work, I generally stay away from until they are over $25, if I have to drive a long way they have to be over $30.