Is your dog currently spilling glucose, is there currently glucose in the urine? If not, your dog will not develop Fanconi until later. The average age of diagnosis is 6-7 years old although some dogs develop it sooner and some later. You will not start treatment until there are symptoms, usually glucose in the urine. I verify the glucose in the urine by a urine test at the vet. You will then need to rule out Diabetes as dogs with Diabetes also have glucose in the urine. Your dog will need to have a blood glucose test and if that is within normal range, your dog has Fanconi, if it is high then your dog has Diabetes. If Fanconi, your dog will then need to have a blood gas test and a complete blood workup. Your dog will then go on the Fanconi Protocol and there is a chart on the Protocol that tells you how many bicarbonate pills your dog will need to take.
Here is the Protocol that you need to have and also give to your vet:
http://basenjicompanions.org/health/images/Protocol2003.html
Costs do vary around the country and some vets do not have the equipment to do a blood gas test. I am in SW OH and my vet does not charge that much for a blood gas test but when I lived in Houston all the tests cost more than in OH.
Some dogs have to take more pills and supplements then others. My Missy, who is 11 years old, takes a total of 17-18 pills a day, including thyroid which some dogs do not need, plus supplements that get added to her food. She takes 10 sodium bicarbs a day, 5 in the morning and 5 at night. She is doing great on the Protocol.