I also had an idea about this, a slightly more accessible version.
Use battery powered stereos. The good 'ol ghetto blaster.
Put in a tape with a song everyone should know, and the "terrorists" press play when they get the stereo/bomb to their objective. They have to protect it till the game ends, and the "counter-terrorists" have to get inside and press stop.
Your idea is much cooler though. What would you charge for something like that?