If you are buying NEW, the obvious choice is the 3500. Its a negligible price difference buying new(I've even seen 3500's CHEAPER because the demand is for 2500 trucks...). The $30 a year difference in registration cost is negligible too. If you can't afford to pay $2 a month to own a new truck and camp... you probably can't afford the new truck and camper.
I truly believe that the 2500 is capable of hauling more than 10K lbs... but I also believe that one should pay the correct registration fee's, no matter what they drive. You CAN get in trouble for driving a vehicle that is carrying more weight then for which it is registered.