One cost is that is directly funded the regime that is now invading a neighboring country, causing more burden on the current military budget as the populace de

One cost is that is directly funded the regime that is now invading a neighboring country, causing more burden on the current military budget as the populace demands support for them, and shoring up local defense budgets as it puts support to the fear that it may be needed at some point in the not-too-distant future. You can't really say what would have happened, but if nobody purchased that cheap gas, I think it's safe to say the Russia of today would look very different, with that being a rather large part of the country's total exports.