I don't usually count the cost of tools and machinery unless they were bought specifically for bow building. When you have the tools, you will find many uses for them besides bows. My tools and machines have done so much work that they have long since paid for themselves in money saved by me not hiring someone to do the work for me. I might add in the cost of blades that need re-sharpening or replacing, but I don't dull them that fast. For cutting something nasty like fiberglass, it's a good idea to keep an old blade handy. As for electricity, if you look at your power tools, you can figure out how much they use in a given amount of time. The actual length of time a tool runs is usually pretty short. Your heat box will use the most, but it won't add up to a lot.
The big expense is in the consumeables, such as wood, glue, tape, etc.
If you're building for your friend, you may not charge for your time, but if you're working for profit, these thing do factor in to some degree.
Again, your time and materials used are the biggest expense.
One other thing, the more bows ( and other things ) you build, the less the cost of your tools will matter.
Just my 2 cents. Or maybe a bit more. :D
Dave.