Have a look at this :
http://www.kam.co.uk/newweb/KAM_PRODUCT_GUIDE_2003.pdfIts the KAM product guide. On page 21 it has the speakers and quoted different values for half of them. I would imagine that there are RMS values though.
They are so cheap because they quote for a single speaker (not pairs) and the quality is not particulaly good. Personally i would never buy a disco speaker unless it had a compression driver for the treble. Its more expensive but the quality is so much better.