cheapest way to do video compression?

[Jeroen3]

Doesn't basically any smartphone processor have this capability?
If you get the entire board, you have the camera, the processor, and the transmitter!

[Scrts]

There is a very strong reason why analog is used there. The digital signal will 'pixelate' and soon die once you hit the transmitter range limit while with analog you begin to see degradation with the 'snow' in the image, but even if it's at the very limit of the transmission range - you still see the image and can turn around.

[accelc2018]

Unless ASICs that does this out of the box can be found, FPGA+SDRAM probably would be the best choice (especially if latency is a concern). As of today, there are FPGA+SDRAM combinations available under $20 on Digikey (single unit price). Whether your algorithm can fit in to the said FPGA is another question which will need some actual testing. Don't forget the cost of power supply. FPGAs usually need multiple voltages to run properly.