A common way of buying saffron in Sweden is to buy it pre-ground in bags of 0.5 grams.
Most saffron rice recipes use "threads" or "strands" which is pretty much useless for me.
What's a good saffron/rice ratio, in grams/deciliter?
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A quick search does not really give a good answer to your question
Have a looksie at this wikihow page.
In any case, I would highly suggest you try to find either Spanish or Iranian saffron, and if possible not pre-grounded.
And skip whatever cheap substitute you will find.
I would be surprised if you find a precise enough scale to be useful in measuring saffron in a kitchen. A half gram of unground saffron will contain dozens if not hundreds of threads, and while ground saffron is less potent, it should still not require very much, so a pinch is probably roughly equivalent to a few strands.