I-75 is of course free. On Florida's Turnpike, the mainline toll plaza near Leesburg is $2.50. If you continue to the I-4 exit you pay another $.50 at the exit ramp. If you decide instead to use the Western Way entrance via TOLL 429/Western Beltway, you would leave the Turnpike at Exit 267A which is before I-4. You won't pay anything additional on the Turnpike but there is a $1.25 toll on the 429.
Thus, total tolls using the Turnpike to I-4 is $3.00. Total tolls using the Turnpike plus TOLL 429 is $3.75.
All toll plazas mentioned in the above discussion are staffed 24/7 if you need change.
BobK/Orlando