Do you have a feeling for the magnitude of cost to implement ADS-B out?
I'd be impressed of anyone got an approved ADS-B out box to market for under £250K, at the very least.
Why?
ADS-B is a high power RF device and, as said above, has to comply with international standards. The standard for them (DO-260B I think) is over a thousand pages long, giving all the details. The path to certification for an ADS-B Out box would really need via Design Authority / Organisation. If you are not one of these already, you can go through the hurdles to become one - this is no small undertaking from previous research, I gave up costing it when it got to £75k. It also take a long time to do too.
Then if you want to make them yourself you, your supply chain, manufacturing & assembly area, and testing need to also be approved. The paperwork, verification visits, etc. would also eat considerable resources as you have to have all the gear ready to be inspected before you can make anything.
So a contract manufacturer would be ideal, but one with all the approvals won't be cheap.
One you have all that you can start the design, make prototypes, then go through the torture of aviation certification (you can't just stick a CE label on and away you go, it must be certified to the international standards). This is lab certification and real air testing, the latter would also need a raft of approvals in case it went wrong and blatted some daft data out that the big boys TCAS complained about.
The only "cheap" way would be to parter up with someone already has the appropriate facilities and authorisations, then make a box that would be suitable add on to PAW. Although I suspect you would need to make a box that could, potentially, take various input sources to make it more saleable. Note for this everything you do design wise etc. must fall within the quality standards of the partnered organisation and you could end up doing all the work and negotiating a suitable percentage to "use" their standing to help with the product certification side.
Remember the PAW bridge is based on a modified off-the-shelf module and is, in relative terms, very low power RF wise. It uses a free to use radio frequency used for a multitude of devices, so lots of people make the packet radio chips that these modules use. ADS-B in comparison is an exceedingly small pool of potential customers, with large development costs.
I wonder what the quote would be for suitable product liability insurance would be too....