Price from your costs, then check the market
Start with what one unit really costs you, including packaging, shipping in and per-sale fees. Add the margin you need to cover overheads and leave a profit, then compare the result with what competitors charge. If the market price is lower than your cost-based price, you need lower costs, a different product or a better reason for customers to pay more.
Margin and markup are different numbers
Margin is profit as a share of the selling price; markup is profit as a share of cost. A 50% markup is only a 33.3% margin. Mixing them up is one of the most common pricing mistakes, and it quietly underprices every sale. The margin and markup calculators convert between the two so you can quote either with confidence.
Before running a sale, use the discount and break-even calculators to see how many more units you must sell to earn the same profit at the lower price.