Having kept a variety of rare breed sheep and cattle over the years, I can confirm that someone will get an excellent price in a conventional livestock market, and that someone will be the buyer and not you.
In a specialised rare breed sale, you might do better but probably not. It's an idea to check prices of the previous sales to see what breeds fetch a good price and which don't. From experience, highland cattle rarely get a good price in a store sale, but I did once get 2nd prize in our local Christmas fatstock sale for a pure bred highland bull. (In the british cattle class)
Highland cattle will fatten quite readily in under 30 months on good grass - the mistake many people make is to keep them on poor grazing, because they can cope with it. They'll cope, but they won't fatten. As with anything - rubbish in = rubbish out. If you want a good price for your product you have to feed them quality. However, another thing that will reduce their price in a conventional market is their horns. They cannot be loaded (legally) with unhorned animals, nor kept with them to fatten further, so they are hassle to someone who has bought more conventional stock. So if you are aiming to sell them for meat or as stores in a market, get them dehorned.
I have sold most of my Highland youngstock and breeding stock through Preloved. I've even sold some from Yorkshire up to the Shetland Islands. But you must have decent stock and good pictures. There's a lot of crap for sale on Preloved - poor quality animals and stupid photos, and they're on there for months because no one wants them. Good stock will always sell if well displayed.
Farming ads is also a good place to sell them on line.
As for your M Laughtan sheep - you need to accept the fact that people keep them because they like them as a pure breed animal with character, and you can never compete with the meat breeds in a meat market. No butcher is going to pay a premium, or even average market price for what is to him a lightweight animal with poor conformation. It costs as much to slaughter a small animal as a large one, and therefore the cost/lb is more with the former. If you're selling pure bred meat then talk to your friends and you'll be surprised how many will buy half a carcase and appreciate the taste of real meat.
If you're wanting to produce something more commercial, then as Coximus says, you need to cross them with a meat ram, and produce something more marketable.