I've been wanting a hive scale for the last couple of years. I've looked at what various suppliers had to offer, and they seemed to be in a $200-$300 (per hive) price range.
I've developed my own DIY electronic hive scale for around $30 and here is a sneak peak video of the setup on my workbench. More details to follow once we get it into the field this season.
You can follow the live (real-time) weights for as long as the experiment is running.