I know there are lot's of photo and image management/gallery plugins for WordPress....and quite a few payment-gateway plugins too.
But are there any plugins that combine the two?
I have a friend who's starting up as a professional photographer and I've used photographers who have online albums that you can order from.
You have your event, photographer takes pics.
They get put into a private (passworded) gallery online.
You can then browse the images online, and order & pay for them online.
They sit online, so if 12 months later you really want a 12 by 9 of a specific photo - you can just order it!
There are companies who offer this service, but in the UK they're about £40 a month plus set up, or they charge per-uploaded-image.