A cross platform webcam library isn't that hard to build at C++. I mean, it's tedious, and having to support multiple different operating systems makes it harder, so it certainly is going to cost a small pile of money, but this is not hard. The pile of money needed won't be all that large. Mind you, I prefer to use something that's off the shelf rather than writing my own, but it would not be hard to write my own.

The hard part of all webcam libraries is all the different webcams running all their different proprietary protocols.