post office now charges extra for anything bigger than a 5 x 9 envelope - there is letter rate, envelope rate (envelope over 5 x 9) and zone rate. Your seller could have put in a flat rate mailing envelope and only cost $4.90 to anywhere in US for whatever fit in box. Your post office may have calculated wrong. 3 oz according to my meter if using a large envelope would be $1.48 no matter where mailed. Are u sure was 3 ounzes. Thats only about the weight of a file folder and 3 sheets of paper. Even a yard of fabric (I just weighted it) was more than 3 oz.