Disney contracted out the actual day to day running of the buses for DME to Mears. So while it is a Disney service, it is done by Mears.
So....a towncar will run about $50 one way or $100 roundtrip, plus tip. A shuttle, run by Mears, will cost you about $15 pp, each way. A cab will be in the $40 area. These figures aren't exact, just ball park to give you an idea.
When I stay at the Swan or Dolphin, I use a towncar service.