Hi Alex,
Chuck provided a source above of course, but we are charging 4.99 as a minimum amount for a bubble envelope or carton (up to 4 ounces). On some occasions for "thin" and extremely "light" items (like the discussed fuel pump kit), we can utilize a business envelope with very thin padding inside (to sandwich the part) @ 0.99, but our local Post Offices want to (will) charge the same as a bubble envelope or carton at the counter (1/4 inch maximum thickness cannot be exceeded, or preferably is less than, for a business envelope to qualify), so we must place the envelope (with a stamp(s) or postage) in the mail slot or box instead.
Regards,
Joe