Just in case you feel you aren't doing enough "number crunching:"
I think you need TWO 'prices' to keep in mind.
The first- the price the customer should see- is a figure reasonably close to the price he's likely to get himself. No $10 aspirins, please.
The other is the burden stocking the item places on you. Now, this is a litle harder to figure- and it goes up dramatically if the item is 'back at the shop' and not on the truck.
I can't speak for every contractor, or every job, but....many times the cost of my trip to the parts house is paid by the customer. Many times the part has already been "bought;" that is, paid for by another customer, and left over/ salvaged from another job.
Other aspects of stocking parts...such as losses /damage over time, are items you control, and need to keep track of.
Sometimes you're better off throwing things away!
