A base product cost is not the cost of making a sale. A durable retail price accounts for production, delivery, channel fees, customer acquisition, exceptions, overhead, and the margin required to keep operating.
Short answer
Estimate every variable cost per order, add a reasonable allowance for uncertain costs, choose a contribution-margin target, and test the result against the customer’s alternatives. Replace estimates with current quotes and fee schedules before launch.
Retail price, revenue, contribution, and net profit are different numbers. A product can show a positive contribution in a calculator and still lose money after advertising and overhead.
List the variable costs of one order: product cost, packaging, seller-paid shipping, marketplace and payment fees, discounts, expected returns, and duties when applicable.
Contribution per sale equals retail price minus those variable costs. Then give fixed costs somewhere to go by estimating how many units are needed to cover monthly operating expenses.