I'm in the process of interfacing an arduino to a load cell from a postal scale.
1 brand new postal scale - $20 on ebay
1 TI INA125P amplifier chip (free sample from TI)
1 10 ohm resistor
Now you have the basis for a great programmable scale that can weigh parts or boxes of parts, do parts counting, accept / reject process control, direct process flow and more.