When we were dealing with renal failure, I created a spreadsheet to track doctor visits and all associated costs breaking them into categories of medicine, office visits, procedures, food. What an eye-opener! I recommend the following guidelines to help you get a grip on costs.
If you're out of work or a senior, find a low-cost clinic or a local veterinarian that will work with you. Ask if a pet prescription can be filled at your Pharmacy then do your homework and check prices. In the case of Buddy's IV fluids and other supplies, the price was less at the local drug store than the doctor's office plus I saved travel time and transportation expenses. It was convenient as well - the staff called when the IV supplies where ready to pick up. I walked 2 blocks instead of taking a bus or train because the distance to the veterinarian's office is a tad too far to walk.
For the third time over the years, I'm checking into pet insurance and did finally find a company to accept both my cat and dog. Other companies denied policies because of age and/or chronic conditions; some would only issue insurance to cover accidents which did not meet our needs.
Since veterinary medicine is making great strides costs are going up and the pet medicine practiced today isn't the pet medicine practiced 10 years ago when Annie was a puppy and Buddy a young cat. Getting pet medical insurance should be looked into as soon as you adopt a pet. It will save you money every step of the way.
Finally, read, read and read!!! Learn as much as you can, make yourself an informed consumer on your pets' behalf and their medical advocate. Not only will you improve their quality of life but you will save yourself a 'chunk of change' along the way.