Free: Contests & Raffles.
I'd personally get the kenetrek gaiters. You should be able to find a site or kenetrek's home site where you'll get a free pair with your boot purchase. I've used damn near ever gaiter, and these are right there in the top ones. They're quiet, fit snug not loose, and have been fairly durable. Worst case, if the buckles strap breaks, sew it on permanently.