A cab, or towncar service, will charge you about $50..one way. Here's the thing to keep in mind. MCO recommends that you arrive at the airport 2 hrs before your flight departure. You could have a long security experience. The longest I have waited has been 25 mins, most have been shorter, but I have seen lines way into the main terminal area. Those poor people had to be in line for at least 45 mins, if not more. And that does happen with alarming regularity.
You state that you don't want to leave WDW 3 hrs before flight departure. And that's your right. You will be saving only an hour if you choose a cab or car service.....and that will get you to MCO with 90 mins to spare. I wouldn't take any chances there....if there were to be a traffic issue, and then you found a long security line..well, you could very well be late arriving to the gate. But, again, that's your choice. I certainly wouldn't cut it any closer than being picked up at the 2 hr mark. I know some go with 90 mins before their departure time, but that gets you to MCO less than an hour before departure...waaaaay too close.