A Content Managed System is probably the way to go; there is more than one photo-based system, Coppermine immediately comes to mind. I use and am very happy with Joomla
I do a fair amount of event photos and portraits, offering free and charged downloads, along with print services. Joomla offers a huge number of add-ins including shopping carts with Paypal as well as other Bankcard processors.
An absolutley gorgeous Joomla based site is Nick Rains:http://www.nickrains.com/