I figured a late reply is better than none, so here goes!
I have ridden the Sling Shot at Magical Midway three times, and the thing still scares me to high heaven. The ride is the most thrilling flat I've had the pleasure of experiencing so far, and is easily worth the money up front. Repeat rides are discounted with the purchase of a shirt or DVD (or you can bring in a receipt from a previous ride).
But, it should be noted that just down the way in Old Town in Kissimme is an even larger Sling Shot (300ft) that is supposed to be even better. I've yet to try it, but I'll get there eventually.