I think pricing differences between the UK and the US aren’t that big. Nowadays, everything can pretty much be done without meeting in person and therefore a designer in France can compete for the same assignment with one in Japan. The difference is more in the specs of the assignment, whether it’s for a big company or start-up, production quantities, technical shoes or simple, etc.
Also, in my experience hiring a freelancer isn’t all that expensive, which may be a downer for you since you want to freelance, but what you basically have to do these days is draw a shoe that fits the assignment and communicate it well much more isn’t needed because the company that will hire you will already possess a lot of knowledge and the factory that will make it will also have a lot of knowledge.