Note the price is $30 each when buying 3 or more. And the price is what it is because we use quality components. The current sense resistors and big power cap are examples; high quality, more costly, worth it.
The BOB is simple, and it works. And it's not just connections and power: It also hosts a relay driver for the spindle. My experience is that opto-isolation causes more problems than it solves, but if you want a compatible open source BOB with opto-isolation, check the PMinMO.com site.
James hosts the single best wiki page about steppers for CNC hobbyists on the net:
http://www.piclist.com/techref/io/steppers.htm Disagree? Tell him what's missing! ,o)