Hey Snml !
According to your question about the public transportation between kinshasa and the nearby cities by bus; first of all I have to tell you that there is no interstate public transportation network in all the DR Congo upto now. But otherwise you can find interstate private buses which links three nearby cities like (Matadi, Kikwit, and Bandundu) but it's more safer travelling by collective bus when planning a trip between Kinshasa and Matadi and even when you want to proceed toward (Boma and Muanda) which are seaport cities after Matadi. Taking bus toward Kikwit and Bandundu are not common and not that safe.People prefer hiring 4X4 "Prodo and others" which can cost you around 200 USD for an up and down trip of 48 hours with driver included.
Bus fares for (Matadi, Boma and Muanda) can cost you around 35 USD oneway trip and you have to pay double for up and down trip.
The public buses are available in urban cities only (Kinshasa, Lubumbashi, Kisangani, Goma etc). Companies running this network in Kinshasa are called (Transco, Transkin, Esprit de vie); a move between one station to another whatever the distance aboard these bus costs 500 FC (Congolese Francs) which worth around 0.5 USD
I guess this will be of help to you
Kane