Ublox
I'm currently using the Ublox LEA-6T evaluation kit (EVK-6T), single frequency receiver with 10Hz, costs USD 349 + shipping. Works with the application RTKLib (open source, developed in japan).
RTKLib also supports the cheaper SkyTraq S1315F, although I have not tested this. The chip has been tested on the michelebavaro blog.
You could take a look at rtklib.com for their supported chips.