if you figure the cost of bottles now a days, your looking at $2 per bottle (based on $24 per 12 without shipping), add in another $.10 for a cork, then your looking at label costs. mine is about $.50 a label.
so with the above figure your looking at what, $5 per just in costs? that's not counting the following questions:
1) how much is your time worth and how much time do you have in that particular batch?
2) how much was your initial equipment? (ie: carboys, airlocks, stoppers, sanatizing equipment, mixing equipment, corker, etc)
It's not hard to get to the $15 mark just on cost alone. What I would do is figure out approximately how many gallons you make per year, then divide that by the number of bottles you project filling from those gallons. Add up all your costs and divide by the projected volume number. That will figure in your mark up costs your start up equipment.
Then it's all about how much profit you want to make. If i were to ever sell mead (which i don't and don't have any immediate plans to do) my time is worth at least a 60% margin. So if my costs were (just an example) $15, i'd add another $9 per bottle on to that for a total of $24.
after that you get into the legalities. how much did your tax stamp cost you? how much are your local taxes? etc...