We also sometimes have to ship large packages, especially wholesale orders. In this case we use the larger floor scale. We think these scales are not suitable for shipping small envelopes because they have more error but for big boxes they are great! The scale we have is the MyWeigh HD-150 (about $120) which can do 0-150 lbs or 60 kgs. If you need even more you can get the HD-300 which can weight twice as much but unless you do freight its rare to ship packages over 50 or 75 lbs.
It too comes with a power plug and a RS-232 serial port, you'll need a USB converter if you dont have a COM port on hand. For microcontrollers, a MAX232 or similar will be handy.