Clark Rubber has these 2ftx2ft interlocking rubber mats which are smooth on one side, and lightly grooved on the other for I think around $12 each, but if you buy more, then you can ask for a discount. I have about 24-30 of them and it will fill up a single car garage – so not exactly cheap, but cheaper than an rcp track.
You can also get cheap interlocking mats from super cheap auto.