Body parts are only available at dealerships. Engine and mechanical parts are interchangeable with Toyota so they are available everywhere. You can use clutch master cylinder from gli, steering rack from passo etc.
Headlights and tail lights are for around 13k. Bumpers are for 7k. Side mirrors are 6k for a pair. Complete doors are 45k. Airbags are for 100k. Fenders are for 9k. Front fog lights for 5k. Oil and air filter are somewhere around 500. These are the prices I know of. In my opinion, the prices are cheaper than genuine body parts prices of other brands. As I remember a friend who got Mehran's original air filter from Suzuki for 1800 a few years back.