take all your equipment + computer and divide by 24 months and divide by the number of times you use your equipment a month +
take all your batteries divide by 12 months +
your daily rate (may be $150- $300 per day?) divide by the number of hours including processing of images, transport time =
your rate ( very simple type of caluation)
its say you own 2 $2000 cameras, 2 $500 flashes, and about $3000 worth of lenses for your job, +4 1gb cards ($130 x4) $520 plus a PC to edit ($1500)
$10,200 divide by 24 months for deprication $417.50 per month divide by the time you shot per month, say 6 times a month= $69.60. That is the cost of using your camera everytime you go out for a shoot.
say you invest about $150 in batteries ( pro camera batteries are more expensive) divide by 12 months and divide by 6 times you use a month $2.10
say you take about 6 hours to edit half a day's work, shoot for 4 hours, transport is 2 hours= 12 hours, 1 1/2 days work. Say you rate yourself at $150 per day, that is $225 for your wages.
transport about $30.
SO equipment $69.60 + batteries $2.10 + pay $225 + transport $30 = $326.70
If you own more expensive gear, the cost cost up, if you have rent, a website, wages for your assistant, all these adds up. if you advertise cost goes up!