While I don't necessarily agree with the one buck suggestion, I think some of us are misinterpreting what its author meant.
He clearly said "each of you" give him one dollar, MAYBE TWO, to "offest the
difference."
It seems from the OP that everyone is driving to the gig separately, so assuming the driver is responsible for the gas to get himself to the gig anyway and would already be driving his own car, and we're talking about the extra cost for now attaching the trailer to his otherwise-already-going-to-the-gig car:
Four people each give a dollar or two = approximately $6.00. The "difference" being the difference in fuel cost between hauling and not hauling, maybe 3 MPG. Let's say he averages 20 MPG without, and 17 MPG with the trailer, 100 mile round trip MAXIMUM, or can we say 30-40 mile round trip AVERAGE. Let's use 40. That's 2 gallons without the trailer, 2.36 with. The
difference in gasoline used in this scenario is .36 gallons. At $3.80/gallon, that's $1.37.
Even at more extreme numbers, say 22 MPG without the trailer and 13 MPG with, and an average trip of 60 miles (not likely) round trip. That's 2.72 gallons without the trailer, and 4.61 gallons with for a difference of 1.89 gallons additional used. 1.89 x 3.80 = $7.12, STILL within the scale of the original suggestion.
My guess is that the majority of their gigs are within 20 miles round trip. So yeah, a buck or two from each member should cover the
difference.
Simple, but more accurate math.