Rear axles for scratch build

[WillsIH]

Hey there guys. Im looking at different axles on many different sites and all seem to be bout $200 for all metal but i can save $50-70 be going plastic housings and metal gears.

Im going to build an enclosed car hauler so my weights wont be exessive. Infact i think the truck will be the heaviest part of the combo as Im also building a 1/16 Mustang to haul around.

Is it reasonable to save money and buy the plastic housings? Or spend the extra and have load potential later?