I run an advertising agency in Pittsburgh, so I might be able to help.
The Pittsburgh Business Times, Pittsburgh Professional Magazine, WPXI.com (has classified ads), the Tribune Review and the Post-Gazette both have classfied sections.
My advice to you would be to place your ad in an unusual place, such as next to the business services category, rather than the rentals category. You'll have less competition, and a more targeted audience.
Good luck,
Claire Devereux Thompson
Sterling Advertising
A http://www.sterling-advertising.com/pittsburgh-advertising-agency.html]Pittsburgh Advertising Agency (broken link)