There’s usually a bus at 6am from Debark to Janamora, which can drop trekkers anywhere along the way, though you’ll probably need to pay Birr100 no matter where you get off. It can’t be used on the return trip because there’s almost no chance of a free seat. Convincing your guide to let you use the occasional Isuzu supply trucks is likely to be tough since it’s illegal, but some trekkers who get to Chenek and find they’ve had their fill of the mountains manage to do it, albeit at an extortionate rate.
The park gate opens at 6am and driving is not permitted before this or after 6pm. Guides can arrange minibus and 4WD hire, though the latter can be very expensive because it usually comes from Gonder. Minibuses can reach everywhere most of the year, but 4WD is required to go beyond Sankaber between July and September.