It's trackless wasteland. The USSR only 'defended' it on the Eastern side to try and prevent escapes. No one is going to devote "hundreds of billions" to do anything there, for any reason. I think you have no idea what you're talking about to the point you can't recognize how ludicrous you sound.
All of it was totally unnecessary until NATO’s meddling Russia started invading neighbors and their remaining neighbors took notice and decided to get off the menu.
FTFY
Well shoot, if it costs nothing to defend the border and nothing will be done for Finnish defense, why in God’s name did the Finns join NATO? Did they just want to weasel their way onto the Russian nuclear target list? Why should an American neocon care how much it costs? We’re printing $600 million a day for Uke corruption. What’s a few billion more for Finland? If, as you say, Finland needs zero upgrades to be able to fend off the Russians, why did the DC MIC oligarchs get Finland in in the first place. No weapons bought, no kickbacks laundered back to DC. You really don’t know how DC operates.