Partly depends on the rug, it's material and construction, and condition.
More for filthy, less for fairly clean to begin.
More for expensive rugs, less for cheap ones.
More for a fringed rug, less for one without a fringe.
A badly soiled silk rug might run $5.00 a sq ft. A not too bad olefin might be 50 cents a sq ft.
Llama skin that needed a lot of re- stitching on the back- Could be $10.00 a sq ft.
Lots of variables.
Gary