$44 per from Amazon; work well... I don't think you are going to find used ones for a whole lot cheaper. They are inherently expensive :\
Pay more $$$ to go longer distances.
But be aware that longer distances means more wattage.
30m is roughly what you should expect.
https://smile.amazon.com/gp/product/B07BHDJKRD?th=1
I have this one and it works just fine. I've never speed tested it, but it worked as a temp connection when transferring data from NAS to NAS.