How should I be pricing my photos? And, what's the best way to mat?

So a consignment gallery in town may be interested in selling some of my work. This would be a first and I have zero professional experience so I am a total n00b here not a seasoned or well-known artist.

I have decided to print my photos at 8×10 and 11×14 and must mat them myself (probably to 11×14 and 16×20) [do some sizes sell better?]. Online, the prints cost about $3 and $5 respectively plus shipping, but I will be doing it locally and expect to pay a bit more. I can get a 16×20 mat here for about $7.50; perhaps the 11×14 one will be $5. So I’m looking at around maybe $10—$15 per photo plus the time and equipment it took to take each photo, post-process, print, and mat. I’m expecting this will end up being a labor of love (i.e., that I won’t be able to recoup cost of my time 100%).

In general and on average, what kind of pricing should I expect? What is a decent gallery/me percentage breakdown for someone in my situation?

Also, what is the best way to mat the photos? They will not be framed. I want the photo to stay put under the mat but I am hesitant about just taping it in place because that seems so permanent. I was going to try to find some plastic casing, and place the mat, then photo, then some kind of backing (what should I use?) in it. Just not sure about how to keep the photo from moving around. Is there an industry standard or something?