The surpass sticker is only 5 and you can load it as you need. It can be ordered on line or purchased at grocery stores
The only problem with the Sunpass mini, that I see, is that it is a sticker and cannot be reused after it has been peeled off the windshield of the car.
You are required to load a minimum of $10 on to the card and top-ups seem to be in minimum $10 increments. Essentially once the Sunpass mini is removed, any money remaining in your Sunpass account appears to be lost at this point since the transponder sticker is no loner functional (once removed). I did notice that if you add another transponder to your account (say for next years trip) that you can transfer a balance. I didn't see any option to request a refund for the remaining funds in the account, although if you were to call and request a refund of the remaining balance they may accommodate you.
Depending if you take the North or South exit from the airport, you will use $3-4 in tolls each way to the airport.
Here's the 3 options:
1) If you don't incur any other tolls in the area, then your total tolls would be no more than $6-8 (if paid cash at the toll booths) from MCO and then back to MCO.
2) The Sunpass mini will cost you $5 + tax plus a $10 minimum load up = $15-16
3) Alamo, National, Enterprise charge $3.95 per day that you actually use the toll roads plus the cost of the toll, so 2days x $3.95 + $6-8 for tolls = $14-16
Notice above that for tolls back an forth to the airport, the cost of the Sunpass Mini and the program offered by Alamo and affiliates are pretty much equal.
Paying the tolls cash at the toll booths is definitely the least expensive.
*** now if you are going farther afield and may incur more tolls or are going to areas that have gone Cashless (Sunpass only) such as the Miami area, then the Sunpass or the rental company's program are the best option.
*** also note if you are a frequent visitor to Florida, a regular Sunpass transponder ($20) could be a good investment for the convenience and small savings on the toll costs (10-15%)