I would say closer to 100-120$/hr that way you hedge against complicated drawings that may take you half a day to review. You are going to need a buisness licence, E&O insurance, general liability insurance, plus a tax guy because your taxes are going to get alot more complicated.
And as another poster stated if you stamp something make sure you were the one who designed it from a blank sheet of paper, if you are modifying existing structures make sure you clearly cloud and rev mark the drawings so you are only responsible for the changes you are making or that you were in direct responsible charge of. The PE I worked under talked about stamping of green or brown field engineering drawings done by someone long gone, I would say for thoes drawings you would need to calculate what it would cost you to retire VERY comfortabley outside of the USA , divide that number by the number of drawings and do one lump sum contract and all drawings go out the same day at which point you will be on a plane. No company will pay that though becuase it would likely be 10-12 million for the set of drawings, they will find some patsy that will take the risk of jail time to work for 60$/hr, if your going to take jail time risk you might as well just sell drugs becuase theres more money in it.
When I got my PE I did not even order a stamp, I wont become a stamping engineer unless im making 120$/hr and my company would have to bump up my wages to that rate for at least a year before I stamped anything as a show of good faith that they are not going to give me the raise only for the period of time they need the stamp. So for me I wont be stamping anything until my experience level is commensurate with that level of compensation. I would actually just like to make that money without ever stamping anything my whole life, it just depends on where life takes me I guess.