There are many good choices at affordable prices at www.balances.com.
I have a Toyo 250g pocket scale. This is good enough for emulsions and developers. I check it occasionally with a 100g calibration weight, and it seems to hold fairly well, and seems to be consistent across the range. It was about $40 or so. The really cheap pocket scales may not be entirely linear (which you think would be important in a high-risk business like the drug trade, which I would guess is the likely market for them).
Generally, the greater the capacity of the scale, the less the precision. If I make a batch of hypo, I need to measure it in two parts. If you need to measure larger quantities, you might want a scale with 500g capacity, but larger than that, and it may not be precise enough for measuring small quantities.