Hmm, might cost more than $50. For maximum effectiveness, I saw we just buy a high powered military grade solid-state laser, mount it to a hummer and park it in the lot. With a couple of mirrors in the stadium, we could direct the beam onto something and vaporize it. Also, as an added bonus, most of those lasers are infrared, so you wouldn't see anything except fire and smoke.
I'm sure it couldn't cost that much.