I'm in Canada, so the prices would likely be different. But basically, it costs just as much as a real photo of the same size.
I buy the bottle cap graphics from etsy sellers, almost everyone has them sized as 4x6 sheets.
So I just upload them to London Drugs (my photo developer of choice), and they print them as if it were a real photo.
So it costs me $0.36 per 4x6 print. If I print duplicates, it's $0.18.
Even if you only need a few images from the sheet, it's still worth it. You could always sell the extra not-as-popular images as a set, or something like that