Murmansk is worth visiting because of its famous Nothern Lights.
The time for visits is from September till April and you should stay 3 days at least to see them for sure.

The cost is from 80 euro per person and depends on the time you spend in Murmansk catching Nothern Lights.
Murmansk and Beyond 29.05-09.06.2021, 07-18.06.2021 from 3 980 Euro per person
Day 1 Welcome to Russia's Capital
Day 2 The beauty of Moscow
Day 3 Moscow to St.Petersburg: Your First Step North
Day 4 St.Petersburg: Palaces and Art Treasures 
Day 5 St.Petrsburg: Imperial Palaces and the Amber Room
Day 6 Sortvala and Karelia
Day 7 Petrozavodak: A Day on the Lake
Day 8 Solovetsky Islands: Last Stop Before the Arctic
Day 9 Murmansk: Kape Town of the North
Day 10 Tundra Majic 
Day 11 Kirkenes
Day 12 Return Home