Hmm. So Miami beach is hard. I was based at KOPF and managed to get a monthly rate from the FBO there. I used to be at Miami exec - but thats now signature - so no thank you.
This past winter i was at Fontainebleau. The daily ramp rate is around $45-$50 per night. Kinda steep. Fuel is $5-$6. I really pre-negotiated a monthly rate - which wasnt cheap either but beats $40x30.
But if you 're going to miami beach - an uber from there is like $20 bucks. The further north you go , ramp fees are cheaper but your uber or car rental will eat into your savings.
So it's a bit of where the curves will cross and how much time do you want to spend in traffic.
To me , it was convenient to operate from KOPF - 22 mins from downtown miami where i stayed most winter.
IMHO - if you're going to be there 1-2 nights - you can try and pre-negotiate 1 night ramp free (call them).
That brings us to KHWO. I was there in 2015 but at a friends hangar for his flight school. So i cant comment on FBO/Fuel/tie-down. But its a training airport + the banner tow planes + everyone who ran from KOPF to get cheaper hangars.
i operated out of there. Not too bad but stay with Miami approach in and out (opa locka is < 4 nm south)
Uber from there will run you $30-$40 to miami beach. It will take 45 minutes. So not too bad but doesnt beat $20 and 20 minutes.
You can figure out whats worth it or not