You have taken one of your sick rabbits to the vet and left the other one that is also sick at home? If they are both suffering from something infectious? And the only vet you can reach charges you such an exorbitant sum for so little and without even telling you what he suspects? I had both my bucks physically examined, blood tests done and neutered and paid 430 GBP for all of it. As far as I can see you urgently need another vet. Maybe somebody here can recommend you one quickly if you tell us the region you can reach. The new vet you should ask to pay in instalments. And take both rabbits at the same time! They both will need treatment even if one seems better than the other. What about the rabbits who sadly died - have they been examined, have they had a diagnosis?
In the meantime, how is your rabbit doing on the medication that was given? The vet prescribed antibiotics, painkillers and something against parasites - should that be given all at the same time? I am not an expert but I was advised to interrupt my deworming with panacur while my bucks were on loxicol (painkiller like metacam) after neutering. What do more experienced people think? Have you been recommended critical care ore something else to syringe feed your rabbits? Do they eat at all? I think they urgently need to be syringe fed if they don't to avoid stasis.
To be quite honest, I don't think your vet is trustworthy and I hope someone can recommend another one. All the best for you and your rabbits!
