Renting a car in Orlando and returning in Miami International. Price, worth doing it ?
The price will depend on your travel dates, the particular car you rent, the agency you use, etc. It does usually cost more to return it to a location different from where you rented it out. Whether it's worth it can only be determined by you. If you are traveling from Orlando to Miami, a rental car is probably the most convenient way to go. But we can't determine if this situation is "worth it" or not. That's for you to decide.
How can we know what the price will be? We don't know any of the things that affect the price, like when you're renting, or for how long, or how far ahead you'll book, or what kind of car you'll get. We also have no idea of what factors would make it worth it or not to you. I wish people wouldn't ask questions that no one can answer for them.
There may or may not be a charge with it. Only you can decide it the charge is worth it to you or not.
Many times returning it as you indicate cost nothing.