I don’t know if the K1 is suffficient for your purposes, but source code and BSP you ask about is free from here (you might need to create a free login):
[url]https://developer.nvidia.com/linux-tegra-r215[/url]
…note that R21.5 is the most recent version for the K1, and that this includes kernel source and u-boot source.
The X1 has the same things available under its most recent R24.2.1:
[url]https://developer.nvidia.com/embedded/linux-tegra-r2421[/url]
Although I cannot answer the price and performance questions others could provide more information if you provide information on what camera frame rate you need and if you require video format conversions.