I have been in your situation.
I opted for euthanasia, as I did not have a competent veterinarian to perform an enucleation/to remove the eye (My cavy-savvy veterinarian was unavailable, as were the Maddocks).
Without a competent veterinarian, the prognosis is rather poor - Not only is there a higher risk that the guinea pig will pass away during/shortly after the procedure, there is also a higher risk of post-operative complications (Which could also prove to be fatal).
If money is an issue, you will have to take into account that there will be post-operative care/appointments, and, if there are post-operative complications, the overall cost could be considerable. You will also have to take into account that there may be an underlying issue/s that may need investigating/attention.
I was also quoted £450-ish from my local veterinary practice.
Do you know whether you are eligible, and/or fall into the catchment area for any of the animal charities that are able to provide/offer discounted veterinary care/financial assistance?