A cheaper TCAS would certainly be a welcome safety net for the General Aviation (especially lower end) aircraft - but no such thing exists, as you know. TCAS, for the display, derives the azimuth of the other aircraft from the multiple receive channels and segmented antennas - making it somewhat expensive - and the azimuth is not very accurate, but sufficient for "looking in the general direction to visually identify" the intruding aircraft. TCAS relies on the rate of closure than the direction of closure.
ADS-B can possibly at some point do what you want it to do - but it will take a few years to work through the issues. Such work IS being done by RTCA Special Committee 186, EUROCAE Working Group 51 and to some extent by ICAO ADS Panel. The FAA and EUROCONTROL are also involved.
ADS-B is in the processes of being operationally evaluated by the Cargo Airline Association in the USA (there is no present TCAS mandate for the Cargo aircraft in the USA) with emphasis on enhanced visual operations and conflict detection at longer ranges than present TCAS. A few European carriers have also done an initial ADS-B implementation for collecting data on its suitability. It is not nearing (i.e., a few years from) interoperating with TCAS yet. One of the issues is the selection of a datalink for ADS-B. There is the 1090MHz link which transponder and TCAS operate in; there is the VDL Mode 4 link (VHF band) that some European countries are interested in; then there is the UAT link in the 960+ MHz band.
There are several places you can look on the web to get more information on the status of the activities.