I've seen many plug ins that allow you to do custom crafting, and it shouldn't be to hard to implement. I also think it would allow there to be end game mules that actually make large amounts of money, and genuine pro mules instead of the new player coming on and making 2k every run for muling.
There should be custom crafting for certain drugs, so you would need things such as sheep, or chickens in order to create it.
Examples:
Xanax (button): 1 button, 2 sugar, and 2 nether warts. Sells for $100
Adderal (firework star): 3 beetroot, 1 wheat. Sells for $120
Crack Cocaine (Ghast...