Keep everything in mind. Fabric, stuffing, thread, paint, wire, poly pellets, safety eyes, stabilizer, everything.
Ex: Wolpertingers- 3 colors, 1/2m base color, 1/4m both secondary colors= 1m at $16/m(fabric shipping cost factored in) +thread at $2/spool+1/4 poly pellet bottle at $2/bottle= $.50+1/4 stuffing bag at $20/bag=$5+felt at $.25/piece+fur(varies, but for the sake of this let's say $4 for the piece of fur)+plastic nose at $.13 for a total of $27.88 for materials alone, not including things that I'd only need extremely minimal amounts of, like paint for the shine in the eyes.
What is your time worth? Do you have education and/or training that you use in your craft? It's up to you to decide the value of your time, but remember that this is a trade that requires experience and (probably) training. It's a specialized job, odds are you want to be payed more than a no-experience required job at a fast food chain.
Ex: Minimum wage in my province is $10 an hour. I try to pay myself around $20 an hour. I have seamstress education/training and 4 years of experience behind me.
This is probably the trickiest one, and it's super subjective. High demand means you can probably raise your prices until your supply meets your demand but it's also a risky game. Go too far and you'll lose your clientele.
Don't really have examples of this, not sure what they could be really. I don't play this game very much.
Paypal fees, custom fees, currency conversion, taxes, all those little things really do add up. Paypal fees are 'only' 4% but that adds up like crazy after a while. If you're using DA's commission system they take (an unacceptable, in my humble opinion) 20%. Keep these in mind as well. If you're declaring your income from your craft you'll have to pay income taxes as well.
Ex: I end up shelling out between $20-$60 in Paypal fees only every month.
Probably what gets forgotten the most. The machines you use weren't free, neither is maintenance for them(mine are $80-$100 in maintenance each every year). Said machines are also not likely to be powered by pixie dust so they also use power. Where are you working? Do you pay rent for your work area? What about getting supplies? Do you have a car that you drive to go to the store and the post office? Or maybe you take the bus and pay transit fare. These are all things that should also be kept in mind to a certain extent. Overhead cost are usually a tiny fraction of the total cost, but should still be thought about
Ex: I pay rent, power, and internet. I use my car to do errands. I've calculated the daily costs of everything which comes up to about $5.95 for rent(my craft room only), $3/day for power, $1.90 for internet, and $2 for gas. So if a plush takes me all day to make I should add $12.85 to make up for my overhead. However I'll be the first to admit I often forget about overhead costs because they're so easy to take for granted.