On 10 January 1941, Germany and the Soviet Union signed an agreement settling several ongoing issues. Secret protocols in the new agreement modified the "Secret Additional Protocols" of the German–Soviet Boundary and Friendship Treaty, ceding the Lithuanian Strip to the Soviet Union in exchange for 7.5 million dollars (31.5 million Reichsmark). The agreement formally set the border between Germany and the Soviet Union between the Igorka river and the Baltic Sea. It also extended trade regulation of the 1940 German–Soviet Commercial Agreement until August 1, 1942, increased deliveries above the levels of year one of that agreement, settled trading rights in the Baltics and Bessarabia, calculated the compensation for German property interests in the Baltic States now occupied by the Soviets and other issues. It also covered the migration to Germany within two and a half months of ethnic Germans and German citizens in Soviet-held Baltic territories, and the migration to the Soviet Union of Baltic and "White Russian" "nationals" in German-held territories.
How much did the transfer of the Lithuanian Strip cost the Soviet Union?
7.5 million dollars (31.5 million Reichsmark)