I did it for a number of years. But, I now live in the middle of the three counties of highest unemployment in the country. If you are in a good area, there should be no trouble. If you like to travel, even better. Find out what others are charging. Don't undercut them pricewise. I find in the northern two thirds of Illinois, it is not well recieved. Some employes think that if you write a 300 I/O in a day, plus all the card connection schematics, then you screwed off all afternoon. Others are wonderfull to work for. I find that the rates are down considerably around here, and that the work is much harder to come by. But then, I have noticed that during election years, things ready bite.
There are plenty of moonlighters out there, and they can really hurt you. There is a guy across the street from me who is a maintenanceman. He moonlights for $8.00/hour, even though he does it in a field with no training. Most of his projects are scrapped before they are half completed, and many others are never fired up if they are completed.
I went into the largest AB shop in the region, and was asked what I wanted. I told them $25.00 hour. They were paying $12-14. Ten years ago I was talking to a local company, since I wanted to get off the road. I was thrilled at the idea of no travel, and was willing to accept $20.00, maybe even less. They told me, "We are paying one guy $30 right now, we'll give you $40!" I thought about it for about 15 seconds before I accepted. Didn't want to seem too anxious.
Know your competition, know the market. Know where to get help to bail you out. (Here is a good place!)
Good Luck, best regards.....kc