Last year, not wanting to pay the $15 cost for commercial mating nuc, my son and I built our own. I meant to post the construction article before now, but better late than never.
The cost was $1 per nuc. This was for the material purchased. $13+ for a 4'x8'x1/2" sheet of extruded Styrofoam and the $1+ tube of Liquid Nails to fasten it with.
From this we were able to construct 16 mating nucs which we used successfully last year to not only mate queens but we stored a couple for replacement use.
Here is the link to the construction description.http://nordykebeefarm.com/forum/forum_topics.asp?FID=6