A wide band sensor helps when mapping the car. When it is connected to a datalogger, then engine problems can be seen before the engine blows. You need to add this sensor to the existing sensors.
Cheapest way is to connect something like this: http://www.innovatemotorsports.com/
Take your pick, there are other makes too.
But it all depends on the rules for the class you are competing in. A programmable aftermarket ecu is a lot easier to map, but will add considerable to the costs of building the car. And the question is, is it allowed in your racing class?