How to watch movies on iPhone 5 without Wi-Fi?

Okay, so I'm going on a road trip this Monday, and I wanted to watch movies from my iPhone (LEGALLY thank you very much) and iTunes movies are too expensive for my taste. I have Netflix, which can work without being connected to Wi-Fi, but it takes up a huge chunk of my very small data plan.

Therefore, I was wondering if there were any legal sites, apps, etc. That can download or sync movies/TV shows onto my phone? And without need for Wi-Fi connection?

It's a longshot, but just thought I'd ask.

You can down the VDownloader+ from the app store for 0.99$, I think.
This app will allow you to download movies from YouTube that you can watch offline later. I'm not sure if you are aware of this but there are thousands of full feature movies on YouTube which are completely legal to download but lie within the gray area of ethical since those movies were pirated in the first place but hey YOU didn't upload them on YouTube.
Your question doesn't specify if you want to watch movies on the iPhone itself or on an external monitor (car DVD player monitor, tv screen, etc) but the app I mentioned will allow you to ONLY play movies and clips on the device itself. If you would like to play them on an external monitor then you will have to jailbreak your device to install an app that allows you to bypass the stupid Mac OS restrictions.

Another option you can try is to convert movies from your hard drive into a format compatible with iPhone (I think mp4 and some avi) then sync through iTunes. I did this with my music video clip library, using RealOne to convert them then sync but I have never bothered with a full length movie; converting and syncing takes way too much time than I care to waste.

Last note from a former Apple fanatic who finally returned to sanity, junk the iPhone and get an android that will let you download all the movies and music you want without having to freaking turn it into a science project. See, on my droid I just download the movies I want from YouTube directly and i have never tried it but you can even rent movies from amazon and watch them on your device (3.99$ sounds like a reasonable price for 3 day rental).

Hope this helped