I got the cheapest SPD-compatabile pair possible at Performance. They were on sale and I probably paid $30 for them? I didn't buy them until after I had been regularly spinning for some months, to be sure they were worth the investment. Then I ended up using the same pair when I bought my Trek and had the platform/cleat type pedals put on it. I'm now ready to invest in a different set of pedals and shoes, but will keep using these for spin classes.

These are the ones I have, or an older version of them
http://www.performancebike.com/bikes...00_20000_52502