I am starting with option C:
Flat session fee and product pricing which includes packages and a la carte pricing. I haven't offered credit toward purchases yet, but it is something that I'll probably do eventually.
However, there is some work put into the package and a la carte pricing. I want to avoid the client who walks away with a single 8x10, hence the packages. Pricing is specifically setup so that there's a discount for going with a package vs. a la carte. Furthermore, there difference from package to package has to be special items that someone may want - don't give away the house with the lowest package. For example, albums, large prints, metal/acrylic prints, and digitals are not in the base package. Do clients want these items? You bet they do, so put them in the higher packages and price accordingly.
Further, a la carte pricing is purposely set so that it's not effective to buy the base package and add those other items; note that all items that are in the packages are listed in the a la carte listing. There is more value (products/price) in moving to larger packages than going with the base package - which is why all items are listed a la carte, so they can do the math and figure that out themselves.
When you go to McDonalds, is it cheaper to buy a value meal or each item separately? If you want a burger and a drink, it's something like $0.10 more to add fries. Once you realize that, who isn't going to get the meal? It's not that the fries only cost $0.10, it's because the a la carte pricing is inflated. This is on purpose. Large corporations spend TONS of money on studying consumer behavior and I'm happy to take advantage of their research and follow their model.