Most shelters have an arrangement with a local veterinary clinic to get discount prices for services and products as a courtesy. That is the route I would pursue, as you will need a prescription for heartworm preventives.
Regarding garlic pills:
Do a quick Internet search on natural ways to prevent fleas and ticks and you’ll come up with thousands of links. You could spend all day researching these home remedies. The problem: As much as we love using natural solutions when they work, many simply aren’t effective at controlling parasites. In some cases these ‘remedies’ can cause more harm than good for your pet.
So before you add chopped up garlic to your animal’s food or bathe her in essential oils, check out our quick list of home remedies to avoid.
Parasite Prevention and Removal Remedies That Don’t Work
Bad Idea: Putting Garlic in Pet Food
Even though a lot of people think this a safe and effective way to prevent fleas, there’s no scientific evidence that garlic — whether it’s fresh from the bulb, powdered or in a supplement — can keep the parasites at bay. Even worse, garlic can be toxic to pets. Garlic contains substances that damage red blood cells in dogs in cats, potentially leading to life-threatening anemia if ingested in large quantities. (excerpt from:)http://www.vetstreet.com/our-pet-experts/home-remedies-that-will-not-get-rid-of-fleas-and-ticks-and-may-hurt-your-pet
