So for a long time the expense of a balance was putting me off from mixing my own formulas, even though I knew it would pay for itself eventually. Then I found via Michael Smith's Azo forum a recommendation for www.balances.com, which has a great variety of quality balances at affordable prices.

I wanted a compact digital balance (no room in my little Manhattan apartment for another toaster-sized appliance like a traditional triple-beam balance), and I settled on a Toyo 250 pocket balance. It has a 250 g. capacity, which seems sufficient for the quantities of chemistry I'm likely to mix in general, is fairly simple with tare function, several units of measurement built in and even parts counting function (e.g., weigh one ball bearing, then put a handful on the scale and tells how many you have), and it really does fit in a shirt pocket, so if I were planning to do some extended stay away from home and wanted to process film on site and mix my own pyro, or make contact prints with my own amidol, it wouldn't be too difficult to take with me. I paid around $46 for it including shipping and a 100g calibration weight. If you already happen to have a 100g weight, it's a few bucks less.