The US has two systems, one the same as ours using the ES capability of the Mode S transponder (1090 ES), the other on a dedicated frequency not available in Europe (978 MHz). This uses a system known as UAT.
http://www.trig-avionics.com/knowledge-bank/ads-b/introduction-to-ads-b/
I concede that however from the Website:
To receive a Traffic Information Service Broadcast (either on 1090 MHz or 978 MHz) the FAA requires that you must first have a certified ADS-B Out transmission. Fitting a Trig transponder provides the easiest upgrade path to secure a certified ADS-B Out signal.So I read that as the ADS-B Position Data is still being broadcast from a conventional Mode S Transponder with ES or an 1090 ADS-B ES transmitter and then the FAA will enable receipt of the TIS on the UAT Frequency. Not sure how they do that must be in the paperwork somewhere.
On the original question;
In USA this is a big thing as ADS-B will become mandatory in 2020.
Does that mean it will get cheaper? 
Given that ADS-B seems to be inextricably linked with Mode S transponders at present, does that mean the US is going mandatory mode S, or are they breaking the mode S / ADS-B link and we might be able to start buying/using simple (cheap?) ADS-B transceivers?
Bottom line is that there is a lot of work going on with electronic conspicuity in Europe and elsewhere. Im not sure if that will result in the kind of cost reductions in units we all desire - one can but hope.
