I had a similar need a few years ago for a Rec. league and I was very surprised at how expensive "simple" scoreboards were (considering how little you can pay for a laptop computer and monitor).
At first, I just spent $25 for a very small tabletop timer that only the scorer could see and bought the "flip numbers" that everyone could see. When I got complaints, I bought a very good portable Daktronics scoreboard from a local supplier....but it was $960. He convinced me not to buy the $600 models because of how they are built. I was able to get three groups to split the cost, so for $320 each, everyone was happy.
One source for the timer only:
http://www.bodytronics.com/page/body.../Timers/CC5022
The cheap flip numbers:
http://www.morleyathletic.com/equipm...le-scorers.htm