This is accurate in my experience. My two self-published history books have sold about 400 and 150 copies respectively (combined print an ebook), with no marketing other than my blog, which occasionally makes it to the front page of HN.

Note that this is purely a 'hobby' project at this scale. Both books are still in the red counting just the expenses paid for cover and interior design, illustrations, and editing (i.e. not counting the many hours of my own time). To make a self-sustaining amount of money self-publishing I would have to sell a lot more copies and make books that can be written with much less effort (e.g. genre fiction).