Personally I think your valuations are way off the mark. You can't buy a shetlander in Thainstone just now for £40! They need to be at least £55-£60 for the ewes as culls (if they are lean), £70-£75 as breeders if they are whole mouthed with sound udders. And these are bottom of the market prices.
Texel ewes in Thainstone last week were £122 a head. They were fat but not huge ewes. Plain Mule ewes which were newly weaned, so not fat, were £78-£81 a head.
The tups (if they are fat) will be at least £80, perhaps the length of £100, if they are leaner then you might only get £70-£75 for them. Don't sell yourself short, at your valuations I could drive all the way down from Aberdeenshire and buy your sheep, put them in a trailer and drive them all the way back. Hold them for the 13 days standstill and then run them into the mart and still make a profit on them! Not fair on you or your sheep.
Be proud of your stock and don't let someone else cash in on your hard work and pride! Best of luck with them though, I'm sure it'll be a sad day for you when they go.