If you have any fabrication capability making some wouldn't be a bad idea... and looking at the prices on those would be cheaper...
Several years ago (like 7) I made my own, went to Napa and grabbed a $12 Semi truck mudflap that was just a sheet and all black, cut it up somehow that gave me flaps that were tire width and went below tire centerline which covers me legal wise... then went to the steel yard and grabbed some 1/2" square tubing with 1/8" wall I think and another short piece of tubing that that fit into and a couple scraps of 1/8" plate. Cut some pieces of the smaller tube the width of the flaps and found a spot on the frame that wouldn't get in the way of the leaf springs or shackles (not many options...). Then put a short piece of the bigger tube on a plate and bolted it to the frame, then used more of the smaller tube and connected the two, drilled a hole for a 3/16" or 1/4" quick connect pin (kinda like for a tractor 3pt). Those flaps have taken more abuse than I would have expected being welded with a harbor freight flux core welder... they've hit trees, held up the rear of one corner when the shackle hanger broke off... and I think cost me around $20... Sometimes I forget to take them out when offroad, and once forgot to put them on on the road and got pulled over, got a REALLY funny look from the cop when I asked if he wanted me to put them back on on the side of the freeway... he said no for some reason...