Also, if we're looking at timing systems, how about this:
http://www.RcLapCounter.com/ ? Had a nose around on the web, and it seems to have got universally positive reviews, while costing vastly less than the AMB stuff. I know you can't use the AMB transponders with it, but given how cheap it is by comparison we could have guest transponders for visitors. Looks like you could get a new working system for $350ish, plus transponders.