My frame of reference isn't huge, but my experience has been:

1. University (student fitness center) only had clipless pedals (spd) for the instructor. All others had cages.

2. Local gym has two bikes in the spin studio with clipless (also spd) -- the instructor's bike and one other. All the rest have cages.

In both cases, only a few of the instructors acutally use the clipless pedals. My road shoes have Look-style cleats, and my mtb shoes are spds. Most of the time I end up spinning in running shoes and cages because I'm not always very good about cleaning the dirt and mud off of my mtb right away!

I'm not sure how the cost compares, but I'd like to see all of the bikes with the same dual-sided pedals that the instructors' bikes have -- one side with cages, the other with clips.