Best RFID Technology for long range detection?
Can you make it compatible with ChampionChip (now merged with MyLaps)?  Many runners have their own chips, and that would be a good standard to work from.   You can pick up 

In response to the comments and answers about the applicability of this technology to racing, I can say that I've run at least two dozen races with RFID tags, and have never had a problem with tag collisions, misses, or accuracy/finish order.  

For redundancy, use two mats, and program in the rate at which runners are crossing. Then, if the first mat has a problem, you can use the second and extrapolate the time to cross the line. 

Find a race that uses disposable chips, or just keep a pair from your next race, and see what you can come up with.  Alternatively, this site sells personalized tags.