If someone puts their own free time and effort to make a mod, they should be allowed to sell it. If you want to spend your free time copying that mod, please do.
You're not entitled to free labor, because you feel like it. It's a game mod, it's not a life necessity, playing games with out mods works as well. You are telling me that people that pay several hundred dollars for a VR headset can't afford to give someone 10-20$ for their work.