Summers are brutally hot and humid in FL.But, you already know that :) Best of luck with the move!

Do you know what that much humidity can do to a house?  

Yes, the bathroom is incredibly humid because they turned off the fan above the shower because it "made a high pitched sound."  

It's not so much a question of what is better - laminate or vinyl (plank or sheet), but what types of flooring are applicable to your situation.While quality laminate (AC3 - AC5) offers a "good looking", functional floor for the price, it does not handle moisture well and can be noisy for tenants below (depending on the sound deadening measure taken in the floor/ceiling boundary).Vinyl tends not to mimic wood as well as laminate {if that is the look you seek}, but it is non-organic, so a good fit for humid or wet areas (bathrooms, laundry rooms, basements, direct over slab, etc).  

Summers are unbearably humid, with tons of biting bugs everywhere.

IMHO - shell out the $1500 for the unit and try to get a bump in rent and/or a 2 year term [it should be easy since it's brand new inside].Indy summers are very humid and tenants get cranky without AC.  

In your area heat thunderstorms humidity etc.

Also I work in an office building as an engineer and what the definition of comfort is for almost any office is 70-75 degrees and 50% RH (relative humidity), so its safe to say that your tenants are right in that zone and should have no complaints.

The mirrors  in the room would fog up from the humidity. just saying LOL

@Mike Vanover When you are saying you are having water issues is it just water coming in or is the humidity just higher in the basement (maybe unfinished)?