Question for con artists

I'm starting to look at selling at a convention, and I had a question regarding the prints. What's are you guy's favorite site or place to print them? My local drugstore (jean coutu) sells the sizes I want for about 15$, and since the average price for a print in a con is 20$ im pretty sure there's a better deal somewhere... Or do you guys just not profit that much? I'd love to know Thanks!