Temporary Florida residents such as the OP can get a FL driver's license and require one in order to register and insure a vehicle purchased and used in the state. You will need to go to the DMV with your passport/visa and proof of address each time you visit the state, and first time you will likely need to take a test. The license will have a validity same as the entry date and time limit you were given on your I-94 (used to be a card stapled in your passport but is electronic now) by immigration on entry (typically 6 months max for B2). I assume the DMV has access to electronic I-94 records? Used to be easy with the paper version. So it's a bit of a pita getting a new license each visit but that's the only way to my knowledge. I have friends who do/did this in order to keep a FL registered car at their condo.
Tip: in between visits you should get a friend to drive the car every month to keep it charged up and to stop the brake discs rusting up (and store it with the parking brake off or else the rear pads can rust themselves onto the disc). Ethanol gas doesn't like high humidity either so keep the tank full when not in use.

..... OP does not have a visa as a temporary resident - he enters on the VWP with an ESTA .....

If you want to get a Florida Driver's License
If you decide to officially establish Florida as your primary state of domicile and obtain a driver's license, you must visit a local driver license service center (like the FLHSMV) in person and provide the following documents: [1, 2, 3]

• Proof of Identity: A valid U.S. passport, birth certificate, or legal permanent resident card.
• Social Security Number: Your SSN card, W-2 form, or pay stub.

Your references are for establishing FL as your primary residence, which is not the case here. B2 or ESTA, both temporary.
If you want a DL as a temporary resident a B2 definitely works per my friends experience. Will an ESTA also work? My guess is yes. Is an I-94 granted on entry? If so, it will have a max duration of stay so that would be the DL validity I assume.

As you say, you are guessing. The DMV site indicates a license is only available to someone with a legit visa. ESTA is the waiver of the issuance of a visa.

But then again, the FL state highway safety/motor vehicles website just calls out the I-94. I assume they do that because that's what actually gives you legal presence in the country.

So, under your scenario, the OP would be able to get a license good for 90 days on each visit, less, of course, the time spent making the application and taking the test. And would have to go through this procedure every visit, bringing attention to the fact they may be pushing their luck a bit ….

If the OP stays more than 90 days, then he would be driving without a licence and insurance.

I tried this when I first started visiting FL. The main issue is not the legal ability in acquiring a DL, it is finding staff who knows they can issue one.

I banged heads with Sarasota DMV on quite a few occasions with staff who insisted that I need an SSN. Rather than attempt to find out the actual situation they would just say they weren't aware of any non SSN exemptions and then give the cold shoulder. Eventually I found an older employee who had spent time in UK and had made himself aware of the regulations - which was handy because, 18 months after first contact with them, I was by then a GC holder awaiting an SSN. He knew about the reapplication grief required upon every subsequent return trip.
I ended up chasing my SSN (which is another story, apparently I was issued with two in the end but have never known the second number...), as it was still going to be major hassle getting a DL without that SSN.

I went though all this believing my car insurance would be cheaper

I have a B1/B2 visa so read up on all the possible ways of obtaining one and having a Florida address valid visa and TAX ID number this is certainly possible so I studied the theory exam and made an appointment and went to my local tax office and took and passed my theory test, they called me through to process my license where the staff had to call for help and we found out that although they could issue me my license it would expire when my I-94 departure date stated i.e. six months at most meaning repeated renewals so totally pointless really.

Turns out my insurance with Progressive isn't much different than anyone else's with a Florida driving license and in most cases cheaper as I have a clean driving history, Its expensive in Florida regardless of your license unfortunatley

Like otherers have stated, if I were the original poster I'd be more concerned with overstaying my than car insurance.