It takes a lot more than $100 to set up a decent grow operation and even with advanced horticultural techniques you're still looking at 6-8 weeks from planting to harvest. By contrast, it takes very little money and not very much time to shake and bake batches of methamphetamine.
Maybe this was his plan for the return rates:
1. Take in $100 in Bitcoins, flip for cash USD
2. Start $100 cheap meth lab with lithium batteries and decongestants
3. Sell most of the first batch, use meth profits and 'personal stash' to create a larger batch, going on a meth-binge to maintain optimal productivity.
4(a). Move to the ocean to to create meth super-lab, paying off investors and becoming a billionaire
4(b). Get arrested in campus apartment
4(c). Die of heart failure from prolonged methamphetamine abuse
4(d). Die in horrific yet spectacular explosion in your seastead meth-tower while trying to create a statue of Batman from the world's largest batch of ice.
