I am not a breeder so this is from a little different perspective. If you have already had an initial conversation with the breeder and if you really do have a limit on what you can spend and perhaps have to travel to see the puppies, I think it would be okay to ask before you take up the breeders time and yours on something that may not be possible. When you call or e-mail to set a time for a visit, I would just say "I know this is a difficult subject for everyone, but at this point in our lives we do have some limit on what we feel we can pay for a puppy, and so that we do not take up your time interviewing us and we do not find a puppy we love and then not be able to even be considered for him or her, would you mind telling me how much your puppies are?" I think good breeders know the difference between this type of inquiry and one from someone who is just interested in price.
On the other hand, sometimes your upper limit on what you would consider paying may change once you see the puppies
. Plus, I do not know about Great Britian, but in the United States while there is some variation in price based on how well the parents have done in shows, it really is not as great as you might image. Sometimes puppies from dogs who have been in the top ten in conformation are not any more and may be less than puppies from dogs who finished their championship but were never shown as specials. Lots of factors go into how the price is set. Breeders jump in and correct me if you think this is wrong.
JMHO