I think you should look at what the standard rate is for each mile that companies reimburse their employees.
Time is very valuable, and so is gas these days, but it may have to just be paying for the gas privately is something people need to accept as part of the job, unless of coarse we are talking about a rural area and 100's of miles. I don't know what the current reimbursement rate is, but just ask a agency that does alot of driving, like a visitng nurse agency, or something.
There are alot of agencies that use personal cars for travel, and then reimburse the individual.
With the rise in gas I'm thinking of allowing for gas money to those volunteers who go out and ask for donations for our fall festival. Is there a certain way we should document it? Have them turn in receipts and reimburse? Also, sadly, I know there would be the 1 or 2 who got a few donations just for a tank of gas. I want to make it clear that there is some kind of quota to get this benefit. Any ideas??