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There was a floated idea in the 90s for the Soviets to sell Kaliningrad back to the Germans. The Germans weren't big on the idea of regaining lands full of Russians that would cost billions to modernize when they were about to absorb their relatively poor eastern brethren back into the nation.
What if the Soviets had approached Japan about something similar? Russia and Japan have a territorial dispute over the southernmost Kuril islands and I would think Japan would be happy to regain those territories. For even more money, perhaps a reversion to the pre-1945 boundary on Sakhalin could be in order.