I'm putting in another vote for dogbooties.com in Duluth. You can spend $40 on Ruff Wear boots and then when your dog kicks one off and you can't find it you'll be [PoorWordUsage]! Dogbooties.com sells their booties in bulk and they are about $2.50 each. If you lose one you just grab another from your stock. They are well made and hold up fine. The mushers love them because they are inexpensive and tough as nails. One note is that with the glare ice we have had around the metro, booties will be a cruel addition to the dog's wardrobe. As far as I know there are no booties with tungsten carbide spikes.
Another great product is "Musher's Secret". It is a waxy sort of paste that you can put on their pads to protect them from ice, slush, salt, etc.