As far the full retail price, well, that seems insane to me as well...
But the deal here is excellent.
If you take the time to calculate a rough per unit cost of fabric($4), wood($7) surrounding frame[to get a good square shape that looks professional] and a high quality acoustic foam($20), plus screws, glue and staples to put the things together; you'll realize that it would be difficult to build units with raw materials for the price that was offered here. You also save the time, which would probably be around 45-60 minutes each to make them neatly. Compare an estimated $31 each + time for DIY units that are comparable vs. $25 each + shipping offered here.
-Chris