Mudflaps are essential to keeping the rocks and general road-ick off your rig.
As well, they provide a great deal of protection for whatever vehicle may be behind you and no one wants to pay for someone else's windshield.

I made mine.  There was nothing available that would fit my Travco the way I wanted it to --giving me access to the differential and rr fuel tank.

I paid a visit to the junkyard (great places) and spent $5 on 2 huge pieces of rubber flooring.
Brought them home, measured, drilled them to fit the original mudflap hangars and will add (just a bit) of stainless to their edges because I like shiny things.