For weighing completed planes I use a baby scale. Keep an eye out and you can usually find one in the trash for free or at a garage sale for a couple of bucks. Mine was of the free variety.

For weighing individiual components or completed 1/2A planes I use an Ohaus triple beam balance. Not that I need the accuracy but because I have one that I gave $20 for at a garage sale. Before that I used a postal scale.

The bottom line is you don't have to spend a lot to get useful eqipment.

Dave