Ethiopian Airlines flies between Lalibela and Addis Ababa (Birr3224, 45 minutes, twice daily), Aksum (Birr2190, 45 minutes), Bahir Dar (Birr1781, 30 minutes, weekly) and Gonder (Birr4298, two hours, daily).
Bus & Minibus
There are two morning buses (Birr75, four hours) and usually four minibuses (Birr95) to/from Woldia, the last leaving about 2pm. If you're travelling to/from Bahir Dar or Gonder, you'll need to change in Gashena.
A bus departs daily for Addis Ababa (Birr295, two days, 6am), overnighting in Dessie (Birr125, eight to nine hours).
Car & Motorcycle
The more direct route from the north from Mekele was undergoing major works at the time of writing, but when finished it should cut travel times considerably. Until then you're better off going via Woldia, from where it's a tortuous three-hour slog on a potholed gravel road.
Petrol is available in Lalibela.