The pricing is rough but any vet is going to prefer you be on prevention regardless of where you get it than not.
Simparica Trio is a good product. So is Bravecto, though doesn't cover heartworm.
Honestly, the dermatitis, skin infections, intestinal parasites, and heartworm that comes from not being on prevention is one of the most depressing and frustrating aspects of working in vet med. Too many dogs have died early and miserable. I hate how expensive it is too, but the long term costs both financially and to quality of life to NOT being on prevention are so much worse.