Over the years, I've gravitated from charging for "time and materials used" to a "per view" approach to pricing. This is mostly to satisfy the client. Digital too added to my reasoning, since I no longer have film and processing costs.
There are two major considerations for me.
First: If I gonna be shooting a full day, I want $1200.
Second: If I making a single image, I feel ANY photo is worth at least $225, even if I finish in less than an hour.
So, with this in mind, I quote $225 for the first shot in studio or $350 if on location. Then I explain additional views at the same time will be around $75 $100 if there are no major lighting or set changes.
This allows a client to budget for the number of shots wanted, and puts me at my $1200/day goal. For example: a smaller job (half day) of 5 table top views on white seamless in the studio would bill out at $625. For a location shoot, I bill from my door to my door for time. So the harder I work (packing, hauling and setting up lighting), the higher the per shot cost. I spend a bit of time discussing this with the client to estimate the number of shots possible during the day. So if I'm working in a plant with larger products, I might get just four shots a day finished, making the cost about $300/view.
In the end, my invoicing will read something like: Produce 4 color views on location, prepare files, deliver all on DVD with index print $1200 or Produce 5 views in studio, prepare files, deliver all on DVD wtih index print $625. On larger jobs, I'll add charges for seamless paper, assistant, etc.
-Pete