I sold 40 (actually 42) 10 day old queen cells for £80 a few years ago, apparently almost all hatched ok after travelling a couple of hours in an insulated box but only around 20 useful mated queens resulted. I usually expect slightly better results placing cells in my own nucs but if I'm honest I don't seem to get the returns I read about quoted elsewhere, if I graft 40 cells I usually get 35 plus queen cells that survive the cull, after placing these in nucs almost all normally hatch but when it comes to harvesting well mated queens with good laying patterns and no visible chalk etc the final total tends to be below 30, depending on the weather when they're mating sometimes nearer 20.