I spoke to my wife who has been a vet nurse for 30 years with the same clinic and it's owned by a partnership.
I asked her why an xray would cost the equivalent of $1600AUD.
She said a lot of clients don't account for the cost of the anaesthetic and the likelihood of having to take numerous xrays in order to find the issue. If, for example, its a leg break, they will take at least 4 xrays to make sure all potential breaks are found. They don't stop after finding the first break. It's not like they can ask the dog, "where is it broken?" Also, anaesthetics don't last a long time. Especially on bigger dogs. They can't ask the dog to stay still while the xray is being done. If they move or jolt, it has to be re-done. Owners think they can hold the dog while its being done, but as you know, everyone has to clear the room. Someone in this thread mentioned using human medication for conjunctivitis which cost a lot less. She is quite sure it won't work on canines and here in Australia the cost would be a lot less because it's subsidised by the government through Medicare. Don't know how it works in the UK.
Having said that she can't work out why it's cost you so much. Based on that you wrote in the original post and with limited information, it would cost the equivalent of about £300 give or take here.
I don't know if any of this helps, but I guess she wanted you to know, it's not as straightforward as you think.