I have no clue about price. Since they are made in England they may not export them. Citizens there are not allowed to own such things, sad.
I’ll bet you could get one built easy enough, but not sure what type of action you would want if you started from scratch.
Have read that Lilja makes some fine barrels for the purpose. They even make 50BMG barrels.
http://www.riflebarrels.com/products/default.htm
not seen that link so thank you, I’ll check it out right now
as for the UK, that is one of the reason of millions why I left after serving there for years