The closest is probably Kissimmee but it's not a full service bus station and I doubt that many busses go there. Orlando has a full service 24/7 station on John Young Parkway, a few miles west of downtown Orlando. You then would need to take a taxi to Disney World and I have no idea how much that would cost. Another option if you arrive Orlando during the day would be to take the taxi to the downtown Lynx bus station and then take a Lynx city bus to Downtown Disney to connect to free Disney bus service to your resort. That is yet another hassle and a time-consuming option but it would be cheaper than a taxi to WDW. Visit www.golynx.com for bus routes and times. You might call the Orlando Greyhound station and ask what the best way is to get to WDW from there.