For example,if Mdma cost you 3euro per gram,or weed 1 euro per gram,or D-meth cost you 3 euro per gram,What price is good for you,for long term,bussines?
I think this always depends on the contacts and most for all the location!
If I had to choose I would pick any chemical drug that has a farily big local market and is cheap+easy to synthesize while still expensive in retail..like MDMA, Meth, Amphetamine, 4MMC
If I had access to the reagents, any of the 4-substituted tryptamines. The profit is always worth the start up cost, people around Europe have sold individual grams of 4-aco/ho-dmt for 300-500 euro a gram.
No one wants to sell in such small quantaties when you're manufacturing but in reality you wouldn't have to move much of the stuff to earn a decent living.
Even if you didn't want to sit on it for years you could get away with selling these tryptamines in bulk for a good price. There's a synth of the forums for Psilocin and the precursors are readily available from Chinese suppliers.