Twenty an hour is a bargain.
My basic rate is fifty an hour, but is adjusted when a lot of work is required, vs. a little, and may vary with the attitude of the client.
If I have a lot of work to do, such as a recovering, twenty to twenty five an hour, if appropriate quarters are available. If I'm having to do it under less than desirable conditions, the price may go up accordingly. General work, I'll typically go at twenty five an hour, especially if it's just extra side work.
I also look at what others around me are charging, and take efforts not to undercut them.