Kigali International Airport: For a gorilla-trek itinerary, the sensible option is a pre-arranged private driver directly to Kinigi: quoted airport-to-Kinigi taxi pricing is roughly US$60–85. It is far less fiddly than routing through Kigali and worth it when you need to report early at Volcanoes National Park. The budget route is taxi from the airport into Kigali, then a Kigali–Musanze bus from Nyabugogo (about 2 hours, FRw 3,000; departures roughly every 30 minutes), followed by a locally arranged taxi/moto from Musanze to Kinigi. Do not count on this chain for the morning of a trek.
Musanze (Ruhengeri) bus station: Musanze is the real transport hub for Kinigi, rather than Kinigi itself. Kigali–Musanze buses take about 2 hours and cost FRw 3,000; from Gisenyi, buses take about 1 hour 20 minutes and cost about FRw 1,900. Arrange the final Kinigi pickup with your lodge or driver before arriving—there is no rail service or formal airport-style transfer system.