Well, the Magical Express would be the cheapest because it is free. Mears shuttle does not go to the WDW resorts, because of Magical Express. A cab will cost at least $50.00 one way plus tip, and maybe more if traffic is slow.
It is hard to say when your luggage will be delivered to your room, some have indicated just an hour or say and others a few hours. Each time I've used Magical Express I checked in at the resort and went right to the parks and did not get back to my room until much later, my luggage was there both times.
I had good experience with Magical Express and highly recommend the service. Just pack a few things in your carry on that you might need, like a bathing suit, just in case you have to wait a while for your luggage. I have read where some people got their luggage and and took it on the bus (well it went under the bus) but I have not done that so I can not say how that works.