Dick,
This document specifies the Australian requirements for ADS-B, refer to page 12 for the list of acceptable specifications for GPS sources for ads-b
http://www.airservicesaustralia.com/...al-18MAR12.pdf
There are several options available that should be significantly less than the $33k price you nominated, eg:
Freeflight Systems | NextGen Avionics - ADS-B Solutions - WAAS/GPS Sensors
or
Lynx® ADS-B MultiLink Surveillance Systems | Models
Not quite yet available and few technical details:
https://www.appareo.com/aviation/ads-b-out/
The US manufacturers are just getting organised and so expect a few announcements in the next few months.