I don't know much about snake boots, but you could try MOPP boots. They are the chem boots that the military uses and you slip them on over your regular boot. They are ruber and shouldn't leak since they are supposed to keep all chemical agents out. You should be able to get these from a surplus store and shouldnt be to expensive. I have never tried this outside of military exercises, so this might be in ignorant post but just a suggestion. Make sure you get 2-3 sizes bigger then your boot size so you can pull it on.
I have the Muck Woody Armor boots and like them but they're a little too big for my calves. When I walk they slap the back of my legs so it's hard to stalk up on something. I normally just wear my gaiters. They cover all of my foot but my toes. I got hit a couple years back by an eastern diamondback about 3' long and it didn't get through the gaiters. I wouldn't take the chance that a big rattler couldn't get through a pair of rubber boots. I was coming out of a bottom we've seen moccasins at a couple days back after the pm hunt and stepped on a snake. Couldn't see what it was but I was happy to be wearing my gaiters. Kinda hard to sneek out of a place and be jumping around at the same time.
