In the USA I use ebay's standard envelope when possible. My minimum charge for this is $1.25. Due to the restrictions on this service I may have to use First Class Package. My minimum charge for this service is $3.50. However, I do not charge for additional purchases that can ship in the same envelope. For example, buy one item for $3.50, or buy 10 items for the same $3.50 total. Larger items require higher shipping fees.
For items shipped out of the USA my minimum charge is $3.35. Many small lots can usually be shipped with this $3.25. Larger items or many items will require additional postage. An item larger than 6"x9" will have to be shipped at a package rate. For larger packages I generally us Ebay Intl Standard Mail.
I have been a member of the American Philatelic Society since 1977 and try to make my descriptions accurate. Please let me know if I missed anything.