People seem to like the Kelty Cache Hauler
Link I'd think something like that, combined with a big silnylon drybag (
Link) would give you an awful lot of flexibility for not much money.
They used to have cache haulers at Sportsman's I think, which would let him take a look at one before purchasing, if he lives near a sportys. I didn't really shop around - you could probably find a drybag cheaper than that. Add in some 550 cord and you're set for just over half the budget.
