Have you installed a kitchen vent a hood? Is it required?

I'm looking at a rental prospect that has a range but no vent-a-hood. 

Per my inspection friend they aren't "required".

How much all in does it cost to install?

Should I invest the money in this? Not sure why the prior owner didn't have one but they had it set up for years without one. 

Is it crazy to not have one over a gas range?  The prior owners seemed to have no concerns fwiw (not much)