För $50 USD kan man, förutsatt att kampanjen går igenom, få 2st moduler med en lite udda MCU och en Skytraq S1315F på som klarar RTK (med RTKLIB).
http://www.onetalent-gnss.com/gnss-chips/skytraq_s1315fUSD$50 NS-RAW 2pcs Set (with Antenna)
Due to numerous requests asking availability of carrier phase raw measurement output capability, we decided to add an additional perk, NS-RAW, a 5Hz capable S1315F-RAW (RTKLIB compatible) carrier phase raw measurement GPS receiver module with USB interface in the same form factor as NavSpark. NS-RAW is to be used as it is without Arduino programability, due to some technical issue yet to overcome and we prefer not to over-promise. You’ll receive 2 NS-RAW and 2 active antenna* at Indiegogo promotional price.
http://www.skytraq.com.tw/