There's a place in the Chicago area called American Science and Surplus. They have all kinds of crap that no one would ever want or need. Except people like us. Take a look at their website
http://www.sciplus.com/ and I'll bet you could find parts for a really convincing ring that would appear to eminate from onstage for a lot cheaper than $150. Only downside of that site is they require a $15 or $20 minimum on web orders. Or DMXtools could build you one.