Buses running between Tawau and KK can drop you off at the park entrance. Not that it helps you much, since you need a permit and a guide to do anything in the protected area.
Car & Motorcycle
It's possible to drive yourself to the park via the sealed road that runs between Keningau and Tawau, passing by the entrance to the reserve; it's a two-hour drive from Tawau and a five-hour drive from KK via Keningau. A beautifully paved 30km road leads from the entrance all the way to the Maliau Basin Studies Centre, the Maliau Basin headquarters, past the Agathis Research Station, around 20km from the entrance. For anything beyond that, however, you need a 4WD.
4WD & Van
Operators that run tours into the Maliau Basin include 4WD transport in the price of the packages, with pick-up from KK or Tawau. If you've prearranged with the Maliau Basin Conservation Area Authority in Tawau, that office may get a minivan to take you to the park entrance for RM700. In the park, rangers can arrange vans to take you back to Tawau or Keningau for a similar price.