For mailings within the USA I am using the special card & stamps ebay envelope.  My fee for that is $1.50.  If I cannot use this method due to restrictions I will use the First Class Pkg rate.  My minimum shipping fee ifor that is $4.75. This allows me to send out all items in the USA with a delivery confirmation. I do not charge additional shipping fees for additional purchases if sent together to a USA site. Large items requiring a 9x12 envelope require a fee of $4.75.  My minimum fee to a foreign country is $3.35. This is for a #10 envelope and less than 2 oz. Larger envelopes or more than 2 oz require higher fees.  Usually more than one lot can be mailed with the minimum fee. If it is a large item I do use Ebays Intl Standard Mail.   A minimum fee of $15.00 is needed for that.  I am not responsible for custom fees or delays, which can be considerable in some countries. I have been a member of the American Philatelic Society since 1977 I try to send out the stamps as described. If I missed something, please let me know.