Start: Black market - Buy poppy seeds.
Next: Grow Poppy in Paleto or some other place just like weed is grown acquiring poppy sap.
Next: Acquire lime and head somewhere to (unknown at this time) mix lime and poppy sap to make Opium/morphine.
Next: Take Opium/morphine and aquire acid somewhere and mix together to make heroin.
Both heroin and opium/morphine can be sold like all other drugs. Opium/morphine would sell more than weed but less than meth. Heroin would sell about same with cocain? (maybe?)
New things in the city would be poppy seeds, poppy sap, Opium/Morphine, Heroin, Lime and Acid.
Let me what you guys think?