The National Aviary is USA's largest and only independent indoor nonprofit aviary. It has over 500 birds representing more than 150 species from the around the world and brings in over 100,000 visitors a year.
The Aviary has a complex history. It was built and funded by the city in 1952 and in 1999, the city ceased funding and through fundraising campaigns, Pittsburgh was able to save the Aviary and it became owned and operated by a nonprofit organization since.
Admission at the time is writing is just $14 which sounds like a good deal to me. There are 3 shows and you can include them in your admissions, admission plus one show is $19, admission plus two shows is $23, and admission plus three shows and a feeding is $25. Check their website (aviary.org) for more details and daily feeding schedules.