So another clarification is needed from the OP...

Are you wanting tracking for one or a few riders? If so SPOT or similar will be great. Friends have that on their sailboats and I can sit at home and see their location virtually anywhere. Costly for everyone though. It requires a monthly commit.

Otherwise I'm not sure what would be cost effective to stream live data for everyone outside of just getting a cellular provider with mobile transmitters to do it free as a sponsor. Can the event be played up as being worth such a sponsorship?