Blimey I'm getting a lorry and bringing all ours down your way!
Our last batch (last week) averaged £75 per head. These are Charollais crosses, all but two were the weights and conformation required for the supermarkets. (In this case Morrisons.) Our first two lambs of the year, of this same breeding but two of the very best examples, and rather heavier than the supermarkets want, topped our local mart at £127.50 per head. Since then the ppk has dropped by 20%.
I don't know what the marts and market are like down your way, but here you'd get a lot more for your rare breeds selling meat directly at farmers' markets or by the quarter or half a lamb than you would in the ring. The bulk of the buyers who go to the marts are buying for export and supermarkets so there is competition for that kind of animal. There'll probably only be one or two buyers wanting less commercial animals, so less competition and therefore a lower price.