It is actually a little less money to use SunPass. You get a slight discount when using SunPass.
Now, the thing is to make it worthwhile you need to have a trip within 30 days of purchasing the pass to get the $4.99 credited to your account.
Step-by-step
You purchase the sticker at the available places.
Go to
www.sunpass.com, register the sticker and your vehicle, and using a credit card, put money on your account.
It will take approximately 24 hours for your account to be active.
The 4.99 is credited to your account, but it expires in 30 days. The money YOU add to your account does not expire.
So, if you purchase it on your way to WDW (the best place without going out of your way is the Okahumpka service center on the main turnpike).
If you have online access at WDW, then you can activate it during your trip, then use it on the way home.
If you go to
www.sunpass.com, it will explain most everything.
I purchased mine on the way home from my trip last weekend. Since I'm going back on the 23rd, my $4.99 credit will still be good, and I'll get to use it.
Since I pull a single axle trailer, it cost me $14.00 round trip to WDW use the toll roads paying cash, with the SunPass, I "think" it will cost me $12.00 round trip to use the toll roads.