absolute low cost solution (but not the most convenient): the use of Laps Free (www.rctiming.com
Just install a laptop or old computer near the start/finish. Install Laps Free on it which is FREE software, and do the input manually, i.e. by typing in the number of a car every time it passes the finishline, ... which is the inconvenient part.
You need someone to stay at the laptop. COuld take turns.
Advantage of this system is that it also does all the talking: announcing the race, giving start, announcing positions ... You just need to hook up some speakers to your laptop or old pc.
Other advantage is that you can also connect any type of time-keeping-device later on when you get the budget. So you can connect the AMB-system, or Robitronics stuff, or I-Laps ... and still type in manually for those who don't have a transponder.
This is exactly the same solution vr6cj
presented, I know. But he gave the advice to get the AMB-software, which costs a lot too. Laps Free is free.
It is not the most versatile, but hey, you get more then what you payed for, and once used to it, it really functions well