The Chinese seller has replied that he would be able to fabricate LimeSDR PCIe PCB. The seller wants to know how many people would be interested in LimeSDR PCIe PCB. If you are interested in a low-cost PCIe PCB, you can send a message to the seller on eBay:
I suspect that soldering BGAs can be achieved with a temperature controlled SMD station. I happen to have this SMD station which could be used for BGA soldering:
The key point is to control the temperature when soldering a BGA. This is an example on how to solder a BGA:
Please send a message to the eBay seller if you are interested in the PCIe PCB.