I can't speak in dollars or volume, but I visited Katabatic Gear a few years ago. To my memory, the owner had a small office & warehouse in the industrial part of town - comparable to a small auto shop - and one assistant.
Plenty of these operations literally run out of a garage though, and Katabatic Gear used to be one of those. I believe Cold Cold World packs are all still made by the owner.
I have been immensely pleased with my "cottage gear".
It's a pretty wide range, some of them are (obviously) big manufacturers. Others, like Enlightened Equipment, started in a garage. Some of them are still in the garage/living room. Those are the ones that I'm truly interested in helping promote, as they don't have the time/knowledge to do it themselves.
Like Silverstorm, I've been incredibly pleased by the gear I've gotten from these smaller manufacturers. So much so that I built this website to help other people find them.