It appears there is no scheduled bus but trips at the moment by passenger van are regularly organized.
Here is the list of companies that offer such trips:
(courtesy of www.allaboutlapland.fi)
The procedure is to call them and ask when the next trip is, and to reserve a seat, and to arrange a place to meet. The cost is in the area of 2000 roubles ($40).
If you need help communicating with local service providers feel free to ask me by writing to firstname.lastname@example.org
PS. Just got a call from one of the operators, Sergei, tel. +7 921 157 9231, who confirmed that there are no regular buses but trips are organized “on demand”. At this moment he has the trips scheduled for March 5, 8, 10, and 17. The trip from Rovaniemi to Kandalaksha is 3000 roubles ($50+) and from Salla to Kandalaksha 2000 roubles. No particular pickup point but call Sergei and give him your address, and he’ll pick you up. And HE DOES SPEAK ENGLISH!! Since there are about five operators like him you can pretty much get on the bus every or nearly every day.
PPS. A comment from Alexandra: