If you are in Australiia speak to Ian Tate from Aviation Insurance. He does a great presentation on how much you need to do per year and how much to charge on an hourly rate. Puts it in normal peoples lanquage, not the typical mumbo jumbo cr@#p that more technical people seem to rattle on with. He is also a really good fella.
His advice is to run it as a business, not just to get by like you are talking about.