Silicon Chip magazine had a nice couple of articles about 5 years ago describing how to make a receiver and its antenna:
Track Aircraft On Your Own ADS-B Receiving Station - August 2013 - Silicon Chip Online
Collinear Antennas For Aircraft ADS-B Signals - September 2013 - Silicon Chip Online
If AsA wants to pay $10k for each one of these then I'll happily make them for them.