Picture framing is an art and a serious craft. It goes far beyond simply preserving a print or creating a mechanism for hanging. The frame, visually speaking, becomes part of the photograph in that it can bring it out, pick up on someof its colours or textures, or become a distraction. There are many alternatives to traditional framing- lamination, metal prints, so-called frameless frames, dry-mounting on various foam-like materials, however, if you are gonn frm in a traditional manner- do it up right.
There are many types of traditional picture framing styles and methods and various materials- wood, metals, plastics, solid wood and veneers. It can simply be made of 4 mouldings mitered and joined to more complex compound frames, mattes, multiple mattes, "floating" frames and even unique shapes and odd sizes and aspect ratios.
Even in the simplest method, if you can coordinate the colour and texture of the material with the content of the image, you will have a more unique and more sellable and desirable product.
I would not advise you to work at a small markup unless you are selling mass wholesale quantities- you would be selling yourself short.
I won't attempt to create an entire marketing plan or do a detailed tutorial on framing. Many frame manufactures that cater to artists and photographers can supply you with all the materials, ready-made frames, frame components and literature of various framing techniques. Another approach is to align yourself with a local professional framer- a fram shop operator and let him or her do the work for you and mark it up accordingly but make most of the profit on the PHOTOGRAPH- the prints.
Here is a link to a professional picture frame wholesaler (in Philadelphia)-
https://www.facebook.com/American-Picture-Framing-Inc-182073785147178/Here's another one in New Jersey-
https://www.manta.com/mb_45_B40170DY_31/frames_and_framing_picture_and_mirror/new_jerseyOr Googl "Professional Pictur Frames Wholesale and do some more research- I'm sure you can strike a good deal with a reliable source. These companies sell to artists and photographers at a discount so you can mark up fairly well.