weducational mentioned nothing about postage. Which would be 'free' if I was selling something for $100.

Most of us aren't telepathic and it behoves those putting up numbers to justify them. Which neither you nor the main protagonist have done. if postage on top of $100 is included in the calculation that needs to be spelt out. ie What sort of postage? How much insurance? .....

Those figures MIGHT change the situation, but they need to be included in the calculation.