I'm a college student, and I buy and sell quite a few sets of tickets during the year in order to pay for myself to go to games. Anyway, here are a few tips I've learned over the past couple years.
1. Look in classified ads for people just wanting to unload their tickets. Not EVERYONE is trying to make a small fortune on tickets, so if you're patient and watch you might get some good deals. Check out local newspapers and the online classifieds site Craigslist.
Here's a direct link for where you should be looking on Craigslist.
2. Look for Steelers message boards that have ticket forums. People don't usually try and make as much money off of tickets on a board. Just like our Tickets section is almost all tickets for Arrowhead, their tickets sections will be for their home games. Don't let them know you're a Chiefs fan though or they might not sell them to you!
3. Worst comes to worst, check out good ol' eBay. Buy it now prices are usually sky high, but auctions close at reasonable levels most of the time. Be patient, and look for auctions that close at weird times of the day (like early morning or after midnight). Fewer people will be using it then, so your chances of success are higher. If you won't be around at the auction's close, use a bid sniping program like
PhantomBidder to bid for you at the last second. In addition, use eBay's "ticket finder" feature to look for tickets rather than keywords. You might find an auction with a misspelled word that no one else can find.
Here's where you should be looking on eBay.
4. People are right that you can usually buy tickets off of people at the stadium. I've never done it since it's a 2 hour drive for me and seems kinda risky, but I might some time!
Good luck! If you're patient, you'll be able to get tickets at somewhat reasonable prices. You won't likely get them for face value, but at least you won't be paying a 400% markup like you might with scalpers.