You can make an inexpensive 10hz Bluetooth GPS receiver for use with Harry's Lap Timer RaceChrono etc using a Reyax RY725AI GPS module two other components and a bit of solder.

Full instructions here: http://did-it-myself.com/diy-10hz-bluetooth-gps-receiver/

The GPS unit will default to 1hz. For racing applications you want a 10hz update rate. This app makes the configuration easy. Just select your Bluetooth GPS and press the button.

It will also attempt to save the change to EEPROM Flash and Battery-Backed RAM. It should work with any U-Blox-compliant GPS receiver.