I've been quickly scanning this entire topic for the first time this afternoon and I am going to bring up a point that I don't believe has been made yet:
Say LoneCowboy had decided to take the next door neighbor up on his $400 offer. What happens if $500 neighbor (neighbor A) talks to $400 neighbor (neighbor B) about their recent mowing jobs? Over the course of conversation, the price that each paid is discovered. Neighbor A would have been upset! He would likely be thinking: "Why the $100 difference?" or "Maybe I should get somebody else to mow the lot the next time." A satisfied customer thinks that he has been shafted.
I would have done what Brian did. I'd be thinking, "The tractor's at the site and off the trailer, no additional costs in labor, hauling, & fuel...OK, I'll do it for $450. Load up, go home, come back later, and unload...$500." Brian made a wise business decision...the costs should play a large part in pricing. I am sure Brian knows where his break-even point is located.