Japanese vs US Blu-rays

[Kyo28]

Hello fellow HD-fans,

I have some questions regarding Hollywood movies in the JP or US release (both are in the same region now).

My situation is as follows:
I've mastered English well enough to watch Hollywood movies in English. My girlfriend however gets exhausted from reading/listening a lot to English, so Japanese subtitles are welcome for her. She needs to concentrate too hard to follow the movie and that prevents her sometimes from enjoying it.

How I'm planning to handle purchases:
- Hollywood movies that we both enjoy, I'll buy the Japanese BR, so she can have Japanese subtitles (and I can enjoy them too then).
- Hollywood movies that I alone enjoy (Science-fiction, etc), I'll get the cheapest version (US or JP, but almost always the US version is cheapest)
- Japanese movies/series, we'll of course get the Japanese release

Now for the questions:
- I've noticed that for the same BR, I usually pay more in Japan than online US prices. Is there a reason for that? Is it because of the Japanese voice actors that need to be paid or the exchange rate of the dollar-yen?
- I often see that some US BR's have a lot of subtitles, including Chinese and Korean but often Japanese is left out. Are there various versions, among which one where Japanese subtitles are included?
- Do you guys have interesting online shops that sell Japanese BR's cheaply, aside from Amazon Japan?

Sorry for the long post, but it would really help me to get a clearer view in all this.