Well, normally I would say to double your costs, but unless there is something special about these mugs, they can be purchased online through the thousands of ad specialty sites for $3 or less, no setup fee.
I didn't see where you mentioned your time involved specifically in terms of cost. Are you accounting for that too?
Since it is a bulk corporate job, to lower your cost you could make the gift box an option for the client. Charge cost for the box as an add on if they want to pay for it. Make basic (free) wrapping bubble wrap and packing peanuts or mail them out using the dividers that came with the case that was shipped to you. They might be just as happy with no boxes because it is an employee give away. Printable promotion companies don't include gift boxes in the base price. You still need to make a profit.
Unless you want a job... you need to factor in time. Even when it's just "You Inc." your time is valuable. By building in time you will make it easy to step into paying employees to do production while you are selling.
As a general rule, about 25 cents a minute is a good cost for labor. That factors $8/hr plus taxes/minor benefits and ineffiiciencies. Nobody really works all 8 hours each day, no matter what.
You should have an item cost. You should also allocate for defects in your item cost. So if your mug is $2/ea and you have a 5% defect rate, than your mug really costs $2.10/ea. That accounts for your defects which are a cost of goods sold.
Your decoration cost will realistically vary. However, money left over is called profit. So I always tend to go a bit high on this. The key here is to figure out what your cost per unit of production is. Probably you print on a per page basis. So you need to figure out what the worst case is for a cost per page. Divide that by the number of square inches or the number of units you can produce per page. For example, let's say my output cost is $1 and I get 3 mugs out of a sheet of paper. That means that my cost per unit is roughly 33 cents. We'll round up to 35. Now I'm at 2.45 cents per unit.
Next I need to allocate about 3 minutes per mug (which covers overhead, bathroom breaks, chat, etc etc etc). That adds 75 cents. So now I'm at 3.20. At this point you need to calculate your margin. At a minimum you need 40%. Less than that and you go broke. The formula is 3.2/.6=5.33 per mug. That's the lowest you should sell for unless you can change cost somewhere. Typically you want to charge more for small runs.
There are a few ways to charge more without raising prices. One is a setup. Most customers will pay an $18 to $30 setup charge without batting an eye. This pays for your software, ink waste, printer (yes it will die one day), samples, etc, etc, etc.
You might charge a 50 % margin on less than 12, 45% on 12 to 24 and 40% on 24+
that would work out to: $3.20 "cost" and
$6.40/ea <12
$5.82/ea 12-24
$5.33/ea 24+
At the end of the day you need to look at revenue per hour and profit per hour. I did not factor in overhead for rent and utilities in this example. Those are real costs that need to be accounted for. Even in a home business you need to charge for them or you will never grow out of your garage.
The checksum looks like this:
10 mugs, $6.40 ea is $64 in revenue. Add $20 setup and I'm at $84. Let's say I spend 15 minutes doing art prep, 10 minutes getting approval and doing accounting. and then Let's say I manage to multi-taks and spend 2 minutes per mug or 20 minutes on production. That leaves me with 45 minutes in the order for $84 in revenue. My costing data shows that I have $32 in "costs" with the mugs and that means I have $52 in "profit". Of my $52, 1/3rd goes to tax. That leaves me with $34. Not bad. $45/hr in gross profit will grow your business.
If you could do that non-stop you'd do well. But often times you run the order and then there isn't anything to do. You have to cover that cost with profit when you can work. Without the setup you would have made $22 on the order, leaveing you with $14. Pretty crappy. $19/hr in gross profit is a hard way to make a living.
Could use some help in pricing 
