I think if one averaged out the cost of steel nation wide you will be looking at somewhere in the $400 rainge to build a basic tube trailer w/
a say 2000lb axle equiped with 7" brakes. Cheaper if you used angle or pos. channel iron. Wile this is not going to compete with the H/F trailer on price point nor ease of build. It is on a par if one is thinking of converting a H/F to brakes.
The 2200lb Kelsey axle w/7" brakes is between $125 (cheapest I'v seen) and $175 (most I'd spend) and is available in 4x4, 4x4 1/2, 5x4 1/2, and 5x5 " Bolt pat. Or one can use the 3500 axle with 2000 lb springs.
The larger 10" brakes on the 3500lb axle don't build up heat nearly as fast and will out last the 7" units. But you won't get the same bolt pat. variety. The Kelsey Hayes axles are prety much the industry standard and are sold trough most trailer suply outlets. Making replacement parts available nation wide. If one must order over the internet. Make sure that you are geting an axle that is at least compatable with the kelsey parts .
Or you may find yourself unable to get replacements when you need them the most. ... Boxcar...