Hi,
This is why we recommend the slightly more expensive route of getting a culture done when you first take it to the vets.
That way when the results come back the vet would be able to switch medication if needed to one that has a higher effectiveness against the specific cause.
I would ask him why he thinks the bloodwork is needed ( he might have a very good reason after all ) and ask about getting a sensitivity test (or whatever they are called) on a swab taken from the snakes throat.
Just my $0.02. (no refunds)
dr del