If you want something that can actually display the timer to the teams, then you really want to pick up a scoreboard. You can get an XBall specific one from Santech, which is just down the street from you in Tampa, and I think they may have two sitting there already made that someone canceled on at a good price (~$6,000).
If you don't care if the teams can readily see the timer, you can use the Alexpotato laptop software:
http://www.alexpotato.com/scoreboard/
Note that that software is wi-fi enabled, so you can put other laptops in the pits etc that can "sync up" with that laptop and display the same information in the pits (although it can be off by up to a second, but good enough for most uses.)
Lastly you can run it on one laptop and then run the video output out to TVs in the pits, although that is more hassle.
"Official" scoreboards from Santech are sub<$10k new.
- Chris