I just got a Synergy Systems SSR-6Tr timing gps with ublox LEA-6T module, which I heard about from a posting here by Dale Robertson on 12 Dec. 2012, "Finally a (relatively) inexpensive u-blox LEA-6T board in the US" diydrones.com/forum/topics/finally-a-relatively-inexpensive-u-blox-lea-6t-board-in-the-us
However that $35 offer is a one-time only deal (1 per customer). Now I heard about another possibility for high-precision receiver (raw carrier pseudorange output for cm-level RTK), that is the NavSpark project on Indiegogo: www.indiegogo.com/projects/navspark-arduino-compatible-with-gps-gns...
They are using the Skytraq Venus822 GPS chipset and a 32 bit Sparc-V8 CPU/FPU.I don't know whether they can deliver on their promise (2 timing-grade raw output receivers for $50) but if they can, as far as I know it is the best deal going for that category of GPS. They say it is not limited to the US GPS constellation but also works with the GLONASS and Beidou sats.