I've been through this 24 months ago. Adding to Yachtbrokerguy's advice: Firstly, he is correct on the average cost but beware that some brokers are charging hugely inflated prices for the stickers. The 1st 90 and 2nd 90 day stickers (total 180 days) can "only" be purchased through the selling broker. If you buy the 90 day and want to stay longer, you must purchase the 2nd 90 day day sticker within 30 days of expiry of the 1st 90 day. The idea/intent is to give you time to prepare the boat for leaving Florida.... fair enough. Note however that Florida is anal & ruthless in enforcing the 90 and 180 day limit, they will not extend it for any reason including if your boat is unsafe for travel. Neither will they cut you any slack if you fail to purchase the 2nd 90 day sticker within the allotted time. In our case we arranged to buy both stickers from our broker but the broker missed the deadline for purchasing the 2nd 90 day sticker by approx 48 hours and despite pleading to the tax authorities by ourselves and the broker, they refused to issue it and demanded we be out of Florida by the 90th day.... or pay the tax. Since our vessel was not in a safe condition to leave yet, we had no choice and had to cough up many thousands of dollars that we had not budgeted for. We will now be faced with double tax when we finally bring it home to Canada. That said, we are now in no hurry and can legally leave our boat in Florida until the cows come home if we so choose.
Note, unknown to us at the time, there is some very small wiggle room with these stickers if you have a knowledgeable/creative broker. Unfortunately ours wasn't.
Incidentally, had we been in a position to simply go to another nearby state when the bureaucrats pulled the plug on us, Florida would have lost three to four times the value of the tax in local repairs, marina fees, supplies, fuel, etc, etc.
Also, I would like to make it clear I do not begrudge Florida the tax, if you want to enjoy keeping your boat there, it is only fair that boaters pay to help cover the costs of the great infrastructure they have in place for all of us to enjoy. I only resent the layer upon layer of vague, poorly thought out County/State/Federal regulations and their ruthless administration of these rules by bureaucrats who often put their own personal spin on them. This forum is a perfect example of how many boaters find these rules confusing, contradictory and complicated.