I did something similar. The 2x6 "pallet" on top was a late addition to keep the body a lot less flexible for transportation to the upholsterer to work on while I was finishing the chassis. My final cost also ended up being at the $100 mark using some very nice surplus very HD casters from a pottery manufacturer that had gone to....drum roll....China



I also made up a pair similar castered dollys for the front and rear of the chassis: