I've got a pager sized Raceceiver and ear buds that I use. I just put it on PRN (channel 0) and leave it there.
What you get on the PRN channel is their network feed. They are pretty funny during their commercial breaks. The biggest benefit of listening to PRN during the race is that you will get explanations any time somebody pits early, has a problem, etc.
A Raceceiver like this can be bought for about a hundred bucks. It can be bought from any place that sells race car parts. These are used by drivers at short tracks all over the country to get directions from the scorer's tower for restart lineups, etc.
Here is a link to the Raceceiver at Day Motorsports in Tyler: