I paid $57.00 plus tip for a taxi from WDW to MCO about 2 years ago. A one way towncar current price is $60.00 - $65.00 plus tip. Comparable to a taxi and you know the TC will be waiting for him.
Having used DME for an early return to the airport I will mention that it was fine, pick up at 5:30 am, one stop at the resorts and then on to MCO. Both times I used DME I needed the three hour advance pick up. The security lines at MCO were very long, over 45 minutes on my last trip.
Whatever you decide, towncar, taxi or DME, I recommend planning additional time to clear security at MCO.
TJ