just a quick look at Uhaul shows a 26' truck from San Diego to Boston is $9000 while Boston to San Diego is $2700. it's all about what they consider to be the starting point and end point.
even if you have to drive a couple hundred miles to get a truck and then drive it back to your house to load up could save big money. the truck will be empty so gas mileage (while still horrible) will be better than when it's full.