Call up your local animal shelter and let them know you are looking for low-cost vet care recommendations. They may have clinics they can recommend or sometimes shelters have special pricing for vaccines, spaying/neutering and check-ups. Many vet clinics also have payment options so talk to your vet to see if there is any assistance available.
Many Humane Society or ASPCA shelters will treat pets on a sliding-scale, ability to pay basis. Many years ago, my hub was laid off from work, and our cat got sick. We had no money, so we took her to the shelter. They were kind, gentle, thorough, and polite, and did not treat us like second class citizens--and after we were back on our feet, you better believe, we made a donation.
Check with your local big box pet stores. Petsmart and petco both have bet clinics that are very inexpensive for shots. They usually hold them once every 3 months. Give them a call. Also animal rescue groups in your area might have inexpensive vet care too.