A coffeetable book will be published and it involves traveling and taking photos of different churches. I'm really in a bind as to how to rate my services. Initially, I'm planning of charging on a per church basis plus expenses incurred.

What's the ideal rate per church?

Why reinvent the wheel? Why not a day rate (for your time) and ope's? This will include your travelling time which is half the day rate. Check around at international sites (asmp.org comes to mind) at how these are structured. And congrats on your project.

Or go with what i used to do for the lack of rate knowledge. Cost Plus. What ever actual expenses you incure with receipts, then you add a percentage to cover your daily rate, depending on the difficulty of the site, assignment & technical creativity of your value added. Talk to your client and ask the entire assignment route. do a time and motion computation. Will you use your own gear? of the assignment requirement, how much gear you have to take? Will you need an assistant? See, you have to take all these into consideration, and your client will appreciate that you will outline this with his participation.