I've checked with the local shipping supplies store. Those boxes certainly ain't cheap. Why are they so expensive?!? They are just papers and cardboards. Someone should start importing cheap boxes from China and put them all out of business.
I've already marked up my handling by about $2 to $3 to cover eBay/PayPal fees and my time and effort for packaging items and going to the post office. Some bidders and buyers are already complaining and demanding me to lower my shipping & handling for them (AFTER they win the auction.) If I try to mark up the handling by another $2.00 to cover the cost of shipping boxes, bubble wraps, peanuts and other shipping supplies, bidders and buyers are going to start sending me bullets in the mail.