I am not aware of anyone based in South Wales who is retubing so you will probably need to take the Rib some distance. Henshaws and Tilley Inflatables are based in the South West, we are based in the North West.
Cost will depend upon your requirements in terms of strake, handles etc.
I can send you a quotation if you PM your email addressd to me
I took mine from Glasgow down to henshaws for a re tube & didn't regret it your on the doorstep by comparison
You won't regret the drive to get a proper job done