10 adult males and 10 adult females?
You should see if he could do 14 females 6 males. A 1:1 ratio of adult males to adult females will not go over well. From my experience too many males stress the ladies out. 50$ isn't too bad but it's not the best by any means. I've purchased 300+ roaches (30 of which are adults) for 45$ shipped. Just do a lot of looking around, feeder sites, ebay, craightslist, forums etc. You can find a better deal, but it might take a little bit of effort.
P.S. I'm assuming you mean dubia roaches correct?