I have read your suggestions for a anti collision system and it sounds like the existing FLARM system...
FLARM is a voluntarily carried, GPS based warning system and very popular in Europe, since it also includes ground based obstecals for example. It is, however, not officially certified as an anti-collision solution, because this would multiply the price point and make changes very difficult. You can, however combine the system with ADS-B via serial input.
There is a small, lightweight device called the FlarmMouse available which sells for around 600$ and is only about 40g. It outputs via RS232 serial and uses the NMEA-0183 protocoll. See here:
I think I'm going to buy one and start experimenting to integrate this in my longer range fpv eqipment... However the price is still a killer for cheaper systems.
But there might be another option, there is a FLARM module available as an option for certain paragliding computers at approx. 100$:
In the last few days have asked both FLARM and the producer of the module, flytec if they could sell these components individually. But FLARM is a sole software company nowadays and flytec, who produces the modules in licence is not willing to do so either. But after some talking with the development manger of FLARM I got the statement that if there is enough interest so that a company - like 3DR would produce the module for the integration in autopilots they would be willing to let them manufacture a custom module based on their licence. Which would mean we could have their core system for maybe 1/5th of the price of a regular system and we can modify certain details (power supply, connectors, GPS interface, etc) which would be nice too...