Like everyone else, it depends. I didn't have much of a stash at all and I recently got my sewing room back after 2 years of giving it up for my grandson. I spent way too much, probably $400 per month, buying large lots on eBay, several collections that I loved, etc.
I also got a Grace frame, a new Viking, and a Go! Cutter. I don't need any equipment now (uh huh) and I'd have to re-organize for more fabric room. I have only spent about $100 the last month on other stuff and I expect that $100 to $200 will probably be my norm.