I am making my own cards to sell, however, I would like to use some graphics and or backgrounds once in a while without having to make them all the time. Where is the best place to buy graphics, images and backgrounds for a low cost that I can use in some of my cards that I will be selling? Sometimes I just need to add one image or graphic and would like to purchase some but not sure where I can get them so that I can use them in a card that I will sell?
Creative Market is designed for just this purpose. There are a lot of great resources from designers looking to capitalize on their creative overflow.
Veer has been around longer. It's more of a standard stock art site. If you remember EyeWire from years long past, these are the guys.