The url below will take you to a provider who sells single images, has tons of content and start at 10 cents/each.
Just click on the pic set you like, a box pops up. You click what pics you want from the set and add it to your cart. I think there is one producer there that doesn't allow it but the rest do.
L&M has nice amateur types pics and allows one pic to be bought.
There is a $5.00 minimum order on the site so you have to order at least that much each time you shop there.
Buy Single Images Starting at 10 cents each!