The short answer is that it's not really feasible.
The longer answer is: all webcams produce a digital signal from their semiconductor CMOS pixels, while all FPV receivers available can only accept analog signals. All of the webcams rely on the software/drivers to decode the signal that the computer is receiving over USB. Each manufacturer has their own proprietary video codec too, which you'd have to decompile and figure out. There are USB breakout boards available for a possible DIY solution like an Arduino, but it's tiny ATmega328 processor simply isn't strong enough to decode a digital video stream anywhere near real-time. Also, when a digital signal drops, the transmission simply freezes and glitches out, where as with an analog video signal, the screen with get fuzzy with static but you still can turn around before it gets really bad. Last but not least, digital video receivers/transmitters are expensive too starting in the $2,500 range.
Price-wise, analog just makes sense. It's frustrating though, because most webcams DO produce very good looking video, but a lot of that look comes from the software being read by your operating system and outputting a digital signal to your video card and then to your monitor.