Why is the cheap stuff less expensive???? Because it is using formulas that were originally patented by other companies like frontline. Then when the fleas and ticks become immune to it and these companies have to develope a newer product, they release the patents and then these other companies make the product and do not have a dime in research and development.
I work at a vet and 9 times out of 10, the dogs that are infested usually the owners are perplexed because they have been using the cheap stuff and do not understand why it is not working.
If you want, check petmeds.com and see what their price is, maybe it will save you a buck.
Breeding and Training Boykin Spaniels, a True American Gundog