@Kieranglen
Sadly Border collies are frequently affected by hip dysplasia and your pup is quite severely affected based on the radiograph and the hips may even be luxoid (so slack they are dislocated). The following is general advice rather than being specific to your dog as proper examination would be needed to determine the best way to proceed.
There are a number of options but few really good ones. If we start with conservative management with physiotherapy, hydrotherapy and pain relief then some dogs will improve around the age of 18 months of age as joint capsular thickening and infilling of the socket help to tighten up the slack hips and the micro fractures of the rim of the socket heal. Unfortunately not all dogs will improve and some just get worse with time. If this happens then surgery is indicated.
There are two main options for surgery, total hip replacement where the old ball and socket is replaced with a metal and polyethylene ball and socket just like in humans. Hip replacement is normally very successful in over 90% of cases and most dogs will be able to lead a normal athletic life. A good number of bilaterally affected dogs will cope with a single hip replacement. The second surgery that could be considered is femoral head and neck excision (aka excision arthroplasty) where the ball joint is lopped off to prevent bone on bone contact which gives far less predictable outcomes, especially in dogs over 15kg and gives good results in about 40% of dogs and poor results in 30%. Most dogs will function as a pet but may not be athletic.
There are other surgeries that may be considered depending on individual circumstances such as double or triple pelvic osteotomy where the pelvis is cut to allow the socket to be rotated over the ball of the femur. Based on the X-ray I would be surprised if this were an option for your dog as some dogs are too severely affected for this to work.
With regards to costs, I think £3k per hip is a substantial underestimate, but this should be discussed with your surgeon. As an aside, if you do go for a hip replacement be careful who does the surgery. I would suggest choosing someone who has a good track record and who performs at least 12 hips per year as a minimum to maintain competence. Also I would suggest choosing a surgeon who uses the Biomedtrix (most successful) or Kyon hip systems as these have far less problems than the Helica system.
Hope this helps