Prophot is a bit expensive.

Photo stock (Bd Serurier, near La Vilette) is less expensive. www.photostock.fr (metro Porte de Pantin and 5 miutes walk)

I'm also very happy with Sels d'argent. www.selsdargent.com and it is closer to the centre (metro Republique or Jacques Bonsergent; and 5 minutes walk)