I'm a CPA. I work from home. Just me and my computer (and my pinball machine). No staff. Low overhead. Most days I wear pants.
Given all that, I charge $150/hour. I only charge when I'm doing actual work; ie: I don't charge for phone calls and emails, time to the "nearest quarter hour" or anything like that. Mostly I'm too lazy to track my time that closely. Clients that are a little more of a pain, with lots of phone calls and "nagging" will pay a little more. Easy clients get a little break.
I give away a lot of free advice (like here, as well as a couple of other online resources). I don't mind because my best, highest value is what I can offer to people who become clients, and that happens AFTER the free advice. I want them to remember "that Wagner was a nice guy that seemed to know what he was talking about," so that they will call me in the future, or even recommend me to a friend. I have tons of clients that I have never met, who came to me after giving "free" advice.
I've never had to advertise, and I have more work than I can do. So the results speak for themselves.
But that's just me.
