In the USA I use ebay's standard envelope when possible.  My minumum charge for this is $1.75.  Due to the restrictions on this service I may have to use First Class Package.  My minimum charge for this service is $4.75.  However, I do not charge for additional purchases that can ship in the same envelope.  For example, buy one item for $1.75, or buy 10 items for the same $1.75 total.

For items shipped out of the USA my minimum charge is $3.35.  Many small lots can usually be shipped with this $3.35.  Larger items or many items will require additional postage.  For large items I usually use eBays 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.