the most cost effective thing to do would be to get a used wheel already built. slightly less expensive than buying a new wheel would be finding used components (track hub and rim) and building it, but you'll probably spend around 30 dollars on spokes, nipples and tape anyway, plus whatever you get the hub/rim for. a perfectly fine prebuilt wheel can be had for like 70 bucks so it doesn't make much sense if you're trying to cut on costs.