Video is one of the most bandwidth heavy thing you can do while normal browsing on the internet. Gaming hardly uses anything, just sending and receiving movements. For RS, it would also download parts of the world as you visit them, at least in the areas you hadn't been to yet.
The Sprint plans seem to be at 5gb, unless you're using an OverDrive wireless modem. That has the 5gb cap on 3g, but unlimited on 4g. From what you've said you do have a 3g modem, and all of those are capped at 5gb.
But 2gb/5gb isn't anything supposing you don't normally watch lots of videos. If you're on YouTube and you do want to watch more videos, I'd suggest making sure that you're loading them in the 360p or if possible the lowest quality offered, 240p. That will use the least of your bandwidth. Try adding &fmt=5 at the end of your video (ex:
http://www.youtube.com/watch?v=kSX2fN5IP60&fmt=5) and you'll get the 240p version at the lower quality. If you've got a YouTube/Google account, go into the
preferences and set the quality to automatically be low. That should at least put it to 360p, which would use less bandwidth than the fairly normal 480p.
