I ordered a small bottle from Amazon for about $20 shipped. It's concentrated so you'll want a spray bottle and maybe a small syringe as well. You mix a small bit in with water and spray it onto surfaces. The 3.4oz bottle has lasted nearly a year so far.
I was curious because I did some research on it and there's a foreign place that ships it that is not the same as the original. They claim to be the same but they are not.