POM to WDW down the turnpike is going to cost you about $18-$20 in tolls.
It's almost 250 miles and 3.5-4.5 hour drive depending on traffic.
The Miami area uses Cashless tolling so you will need to use the rental car companies Platepass option OR your own Sunpass transponder.
Alamo, National,
Enterprise have the best toll option IMHO.
They charge $3.95/day admin fee + the actual toll cost, but this is only charged on days you actually accrue tolls. So basically only the one day you drive from POM to WDW.
WDW to Universal is a straight drive along I-4 with no tolls as bumbershoot already noted above.
***FYI: it is actually possible to avoid toll roads by taking SR-27 OR I-95 but it is a longer route and traffic gets really crazy the closer you get to Miami.
We tried both and hated it. Bought our own Sunpass transponder and use the Turnpike whenever we visit the Miami area or the Keys now.