I purchased a new Escali digital electronic scale off of ebay for $28 delivered. Measures 0-25 lbs, accurate to one half oz. It comes with a power supply or can be operated from battery.

You can put a platform (I use a 2'X2.5' light ply board) on the scale before you turn it on, and when you turn it on, it will automatically zero itself with the platform included. Set your plane or parts on it, and get their true weight.