I purchase photo mats in bulk when on sale to save money, and order those that are delivered in reclosable archival cellophane envelopes so that I can mat the print and then return it to it's clear envelope that the mat was protected in originally. I include a "free" business card (which I order online for just the price of shipping) inside with each matted print, as well as a label showing the title, type of art and artist's signature. The art print itself is stamped with artist's information on the back also. The price label is affixed on the outside, so that the envelope doesn't have to be reopened due to a possible price change.
I keep the titles of my work consistent with the titles I sell online so that they are easy to find if the design is wanted in a different format such as cards, mugs, aprons, etc. My business cards include information on the back as to where the prints are available locally and where different formats and products of the print designs are available for order online.
I keep mats on hand, and can print out an occasional print at home if a special request is made. But I find it is less expensive to order prints in bulk online, as long as you stick with a company that you know consistently provides good quality prints at reasonable charge and then keep track of the prices at each site you use so that you can always purchase them when they are at a reduced sale price.