In the age of social media and blog sites making money off what they are recommending, I don't put much faith on the internet as a source. Not being a veterinarian, I wouldn't want to jump into this discussion other than offer the advice listed here which says consult your veterinarian:
Safe use of flea and tick preventive products
"Parasite protection is not “one-size-fits-all.” Certain factors affect the type and dose of the product that can be used, including the age, species, breed, life style and health status of your pet, as well as any medications your pet is receiving. Caution is advised when considering flea/tick treatment of very young and very old pets. Use a flea comb on puppies and kittens that are too young for flea/tick products. Some products should not be used on very old pets. Some breeds are sensitive to certain ingredients that can make them extremely ill. Flea and tick preventives and some medications can interfere with each other, resulting in unwanted side effects, toxicities, or even ineffective doses; it’s important that your veterinarian is aware of all of your pet’s medications when considering the optimal flea and tick preventive for your pet. "
I adopted a street dog when I was in college .. it had mange and other parasites and she was treated as was necessary and made a great recovery. That was 50 years ago, and we've followed that approach ever since. For as far back as I can remember ..... I'm old do prolly not that far
.... that advice has been Ivermectin* for the worms (Heart Guard) and Advantix II for the Fleas, Ticks, Lice, Flies and Mosquitos) ...
* I recently learned here (JoanneF ?) that some breeds have a genetic sensitivity to Ivermectin due to a mutation in what is called the MDR1 gene so, especially if your dog is one of those breeds, testing is recommended. You also need to be careful when storing the pills, chewables, collars, drops as they can be toxic is consumed in significantly larger quantities than the recommended dosage.
As for costs, many local non profit shelters perform vaccinations and you can obtain these medications there at a substantially less cost. Some treatments require a prescription and it saves you the trip to the vet to get one as they have the vets on site.