They have a $50 version that supports raw data. Although, without a high quality antenna I wonder if RTK is even going to help much? >> NS-RAW: carrier phase

They have a $50 version that supports raw data. Although, without a high quality antenna I wonder if RTK is even going to help much? >> NS-RAW: carrier phase raw measurement GPS receiver, max 5Hz update rate, RTKLIB supported S1315F-RAW in the form of plug-and-play NavSpark