> The first thing I wanted to do with my Saab 96 was to establish a baseline weight. The cheapest scales used for racing are over $700,
You can do this for (almost) free if you go to the local dump. They usually charge you based on weight of what you dump by weighing your car on the way in and on the way out.
Just ask them what the reading is on the way out. If you bring a couple of pounds of garbage, it will cost a few dollars at most.