Perhaps it also should be mentioned that accurate load cells are not cheap! :shock:
The basic load cell has strain gauges inside, arranged in a bridge. When a load is applied one of the bridge elements gets unbalanced, resulting in an output voltage. This output is very small (mV) and requires a very good, linear and temperature compensated, amplifier to get it to the range suitable to drive a LCD display. That amplifier is also rather expensive!
You then need a dual power supply for the amplifier. The load cell gets excited from this as well, via the appropriate trip pot and drive circuit.
The exitation voltage is set to suit the expected output range. Set it too high and the bridge output swing becomes too great for the amplifier gain
(~1000) , clipping it. Set it too low and the sensitivity suffers.
I have played about with home made strain gauge load cells and commercial amplifiers, in the kilo range. For gram (or grain) ranges I would imagine the home construction of a load cell is too tricky, leaving you the expensive option to buy one
I would imagine a purely mechanical jeweller's balance scale to be very accurate for your usage. Its not an electronic solution to your problem but perhaps you could pick up a used set of scales, with the appropriate weight set, for a reasonable price.
Good luck