Although I have jumped in, and said that at £42 a carcass, whoever is selling that is either really really nice, or really dumb lol. I do think that there is an upper limit to what I can charge for meat and not feel like i'm robbing folk. Whilst I accept that it would cost the same to buy from a supermarket, I'm not a supermarket, and I like the idea of selling people meat at a reasonable cost, which allows them to make a saving over shopping at the butchers, and allows me to make a profit, and in the case of boxed lambs, a greater profit that I could sell that lamb for live.
The thing is, if we work out our inputs, i'd imagine that it costs me a lot less to produce a lamb than some folk on here (i.e I don't feed any feed to the ewes or lambs AT ALL before, during or after lambing). However, I do cost in my time at an hourly rate, so maybe that would take it back up past those that don't cost theirs (a fatal error).
Having said that, I generally just look at what the going live weight / dead weight price is at that time, add on the fee to kill/butcher it and then a bit extra on top for the hassle.
So if I can sell a fat lamb for £70 at market, and it costs £25 to kill and butcher is properly, and then I throw say £40 on top for the hassle, that works out around £135. So something like £70 a half sounds reasonable. Bearing in mind most carcasses come back at 21kilo dw.
Edited to add - I suppose it also makes a difference how many lambs you have. I'd rather sell a lot, at a bit cheaper, than the odd one at a higher price. The other factor, is by pricing it so highly, it ends up becoming an occasional 'niche' product, as opposed to a regularly used food stuff, i.e at a slightly lower price I might actually sell them two lambs rather than one.