You see a lot of guys that have been employed, maybe as a tradesman, decide to go and become self employed (worst boss you'll ever have), they may have been earning $30 per hour, so they figure they'll be quids in if they charge their time at say $45 PH. The amount they were getting is just one component of the overall cost of providing the service they perform.
Good advice from Glenn, BD, I carry several thousand dollars worth of extension leads to allow me to connect appliances to any of my PATs or measure the items current leakage, they are the necessary Plant & Equipment expenses of doing business. These sorts of costs are why it's really important to understand your cost structure and make sure you are charging enough to cover the cost of buying all the gear, insurance cover, Standards & Publications, on going training, paying tax and ACC (in NZ) as well as making a living.
A really good book written by an Aussie Electrician is well worth a read if you are self employed in Australia or New Zealand ,
How To Escape From Quicksand, you can find it on line easily
http://escapequicksand.com/