I seem to remember Dealextreme used to sell an L1 (1560-1580 Mhz)and L2 (1217-1237 Mhz) GPS Jammer i.e. for both the Military encrypted and Civilian Channels for about $30. Expanding the size of the jamming bubble just depends on the RF microwave power of the jamming antenna.

I have a Model:G30 Cell Phone and GPS Jammer which blocks 850-970Mhz CDMA/GSM 1560-1580Mhz L1 GPS and 1805-1930 Mhz DCS/PHS with 3 handy SMA microwave connectors which can be fed to tuned microwave Amplifiers.

It does a nice job at blocking GPS and older GSM 2 and 2.5 cellular phones . Once folks realise how easy it is to block GPS signals they begin to appreciate old school navigation.

L1 Spoofing is relativity easy as well as the GPS signal format is available on line.

http://www.navcen.uscg.gov/pubs/gps/sigspec/gpssps1.pdf