I cant recommend anything that's over the counter as in my experience nothing works.
I do think you are paying a heck of a lot and can get that right down without resorting to over the counter though.
Do your vets do a monthly plan? I pay something like £17 a month and that covers all her flea and worming treatments, vaccinations, (only 25% off kennel cough vaccine) 2 health checks, a percentage off treatments, nail trimming and a whole host of other things that I can't remember off the top of my head.
This year my dog will be having the 'new' Bravecto injection which will cover her for the whole year, but I have no idea how much it will cost, but it's covered in her monthly plan.
My last dog I paid the prescription charge but was prescribed for the whole year (4 x treatments) and then I purchased Bravecto and wormer from Viovet which made covering my dog a whole lot cheaper. She was also allergic to pretty much everything and couldn't have any topical treatments so we had to go orally or injection only.
If you can't get a prescription for a year's treatment have a shop around.Jollyes have community vet clinics that are extremely cheap. Animal Trust vets are a non profit (I think, so don't quote me) they dont charge for consultations, they are incredibly cheap too.