All you need is one yard of a good, stretchy jersey, and 30 minutes of your time.
Cut 1 rectangle for the waistband, your waist measurement minus 5"x 8"
Cut 1 rectangle for the body of the skirt, your hip measurement minus 5" x your desired length plus 1".
Use a serger if you have one. On a regular home machine, use a stretch needle (it has a blunter tip than a regular needle to prevent it from attempting to puncture those crazy, spandex-y fibers) and the stretch stitch (pictured below), paired with a zig-zag on the edge to prevent it from rolling, which can add extra bulk to the seam.
Sew up the back seam of both waistband and skirt.
Fold the waistband in half, wrong side to the inside, and sew it to the top of the skirt, matching the back seams together.
Slap on the hem of your choosing, and you've got a skirt!