About 200 days per year work and in-between 100 - 300 a day turnover.
Then look at expenses, sickness, broken equipment, holidays, tax, ni, insurances,etc, etc...
Hope this helps a little.
People get jittery on here when money is mentioned...but suffice to say that if you plan your working year at about 200 days of actual work then you could be doing very well if you price well.
Cheers
Dave.