I'm trying to find the bus/Amtrak fares for the past 10 to 20 years.
You are probably already aware of the library research guide for your class at http://library.uhd.edu/mba6212.
I suggest you use a resource called Statista, and although it is a free Web site, not done by government, it does appear to meet criteria for credibility. It had charts on both bus fares and Amtrak fares. See:
If you want to look more at government statistics about transportation, see the site of the Bureau of Transportation Statistics at http://www.transtats.bts.gov/