Stay away from stocks, its all falling these days so it won't be long they won't be sending you $28/day for it.
Mining instead will be but the electricity cost is the one that you'd be dealing after. How many GPUs can you buy with $4000? I would assume 5 at least and start mining.
You can buy used GPU. It will be about 300MH for $4000 if you are lucky. Today it can bring you about $20 without electricity bill. I cann`t calculate correct because it depends on GPU model, but i think it will be about 1KWt.
So calculate it by yourself. And you have to test GPU yet or pay to specialist that can test it. And construct and configure rig.
I cannot say that this is passive income.
$20 is a decent amount in the South. It's the durability of the GPUs that you will need to worry about when mining because without proper maintenance and cooler, it will give up and you not achieve a breakeven.