My normal shipping fee in the USA is $3.50. This allows me to send items with a tracking number at a reasonable cost. I do not charge for additional lots purchased and paid for at the same time. I also use the eBay Standard mail for which I charge $1.25. Larger envelopes do require more. My minimum charge for shipping outside of the USA is 3.25. This is for a #10 envelope for up to two ounces. Usually several small lots can be shipped for this fee. For lots requiring larger envelopes additional fees will be required and most likely package fees will be required.
I have been a member of the American Philatelic Society since 1977, and try to have accurate descriptions. If I have missed something please let me know