Nobody tells you this. So if your passport is taken, ask where and when you have to go to collect it. You may need a stamp at the police station in Kayes too, but this seems fairly arbitrary. On many routes, you also find more rustic minibuses - sometimes, rather misleadingly, called cars rapides . These are battered, slow, crowded and worth avoiding if possible.
Fares are reasonable.
Buses are about a third the price of bush taxis, and minibuses are somewhere in between. There's normally a small extra charge for luggage. Some smaller outfits have cheaper deals available. We encourage you to verify any critical information with the relevant authorities before you travel. This includes information on visa requirements, health and safety, customs, and transportation.