I’ve been using the Gemini 20 milligram scale for over 10 years. ~$30 USD and can accurately measure down to about 20mg. Might be able to find something slight more accurate for around $100 but the difference won’t be noticeable unless you drop several k on a lab grade scale.

Edit prices went up a bit, my bad:

https://www.amazon.com/American-Weigh-Gemini-20-Black/dp/B077KC8D8Y/ref=mp_s_a_1_4?crid=39KIIRUER20G7&keywords=gemini+20+scale&qid=1648167968&sprefix=gemini+20%2Caps%2C119&sr=8-4

Here is a little kit with flakes of metal that weigh down to 10mg so you can be sure you are accurately measuring small amounts:

https://www.amazon.com/Calibration-10mg-100g-Precision-Stainless-Jewellery/dp/B085N5NH8Q/ref=mp_s_a_1_4?crid=25H7PBMG0UFOJ&keywords=mg+calibration+weights&qid=1648168069&sprefix=mg+cali%2Caps%2C93&sr=8-4