I can offer no advice/comments on the matter but only to remark that I usually print my own pictures.
I saved up and bought a nice color laser printer
(refurbished) that can manage up to 12 x 14 prints.
The printed pictures/portraits are well adequate and and of acceptable quality that easily surpasses the quality output of such places like Wal-mart, et al.
To me the expense (just under $2K) was well worth it.
Now, $2,000 may not be in your budget, there are other color laser printers (or even good ink jet models) that are quite affordable. And if you are looking to do this for a profit, I don't see why you couldn't generate the revenue to acquire one.
Also, a side tip: as part of your "business" you might be able to write the expense off come tax time.