I would chime in that the difference in production work and studio work makes a huge difference.
A hand crafted mug that has a lot of additional detail and time involved might be priced substantially higher as more of an art piece than a production mug that is thrown in a few minutes, trimmed in a few minutes and a couple of minutes of a 2-3 hour glazing session along with a small corner of a kiln (our 9 cf kiln cost about $6-7 to fire by the way). 30 seconds more of bottom sanding an it is ready to go out the door somewhere.
This production mug is still going to be a beautiful handcrafted mug (may well have a little carving or slip work) and gleaned from hours of drawings, testing and other design work by the potter, perfected for production runs and will be priced at say $25 retail.
A $12.50 split works out OK for the potter and selling direct to the public will earn $15-$17.50. Direct selling through decent size fairs cost about 30-40% in expenses (but you will get some show labor at slightly above min wage out of that :-) and could increase north of 50% if you have a string of show failures and have to eat some additional cost somewhere. Like Mark said, it is going to be a moving target trying to attach direct expenses to individual production items if you make and sell many.
One thing I would warn is not to take more involved artistic studio work that is done on a functional piece of pottery, like a mug, that you invest a lot of time in and then price it like a production piece or you will have trouble making it work.
Not sure I agree with your pricing based on experience. A subpar mug should not go out and if its a quality mug then why should it not be priced a what is perceived to be the market rate? A famous potter may command much more but you are advocating pricing at well below what I think most folks see the market rate of 20-25 bucks for artisan made handcrafted mugs. I think this is what the artisan market sees as an average price for a nice hand thrown mug (I am assuming your talking about hand thrown mugs and not slab work).
I would argue that the adjustment is made if you're honest about the work and only sell beautiful mugs and trash the rest. This means that a new professional is going to have a much higher failure rate than a seasoned pro and make less because of this. The mugs that hit the market though are all of high quality and priced right. Everyone is served as the market is not depressed and the seasoned pro is realizing some additional perk of his/her years of hard work.
The business forum moderator, Mea Rhee, did a fantastic hourly earnings project that was published by this sites magazine and Mark C's and others threads offer of lots and lots of details on making a living at this.
Good luck with your first wholesale customer!