An NPR station can operate cheaply or can have a big payroll. By going the inexpensive route, you simply run NPR shows as-is.
In NYC, 91.5 WNYE-FM has NO local programming between 10 a.m. and 7 p.m. On weekdays, it runs "1A," "On Point," "All Things Considered" and a few weekly public radio shows like "Hispanic USA" and "Zorba Pastor on Your Health." It doesn't even have a local person do news or weather. The NPR hourly newscasts run in their entirety. WNYE-FM is owned by the City of New York. It runs cheaply and never asks for donations.
On the other hand, NYC also has WNYC-AM-FM, run by a public corporation. It has a large news department and two local weekday shows from 10 a.m. to noon and noon to 2 p.m. WNYC also has weekly shows that get syndicated on many NPR affiliates, including "On The Media" and "The New Yorker Radio Hour." WNYC probably has the largest donations of any NPR station.
I'm sorry to hear two of Pittsburgh's public radio stations, WESA and WYEP, are struggling. WESA is mostly NPR news and info, WYEP is Adult Album Alternative. And then there's WQED-FM, Pittsburgh's public classical station, that also seeks donations. But as I said above, there are plenty of ways to run all three formats cheaply if you use a lot of national programming.