I agree with the Ivermectin replies. The doc can work out the proper dosage and save you a load of money. I'd alternate with Fenbendazole (Panacur/Safeguard) just for good measure.
Picking up poop regularly (at least weekly!!) will hugely reduce the re-infesting problems too.
Fleas and ticks are harder to get by 'cheaply' but with just 6 dogs I think you can do it pretty easily. Diatomaceous earth (food grade!) is safe for their houses and even for them to eat, it kills all external parasites. Spraying the yard and especially the borders of the yard helps a ton. The clinic I work at recommends Triazicide, it's at Wal-Mart and Lowes.
Frontline must be costing you an arm and a leg for those dogs!
HTH
