The Pittsburgh area is home to 422Sales. Bring your budget and you should be able to get a very, very nice bus. It will cost $100 for a bidders number then the premium after you buy a bus is 6%. The buses there sell pretty cheap. Look at the bus market reports on there website to see what some buses sold for at previous auctions.
Heres there website:422 Sales Home Page
Craigslist, Ebay, and government auctions like GovDeals are all decent ways to buy a bus