I-75 of course is completely free all the way from Michigan to Florida.
Florida's Turnpike has a mainline toll plaza near Leesburg that will cost you $2.50.
Once you get to the Orlando area, there are two main routes to Disney and which one to take depends on where your hotel is located or the theme park you're going to if you're headed to one of those first.
If you stay on the Turnpike to the I-4 junction (Exit# 259), you'll pay another $.50 at the exit. If you get off the Turnpike earlier at the Western Beltway (TOLL 429, Exit #267A), there is no exit toll but you'll pay $1.00 on the 429.
So bottom line is that you're looking at either $3.00 or $3.50 total. Not too bad.
BobK/Orlando