It makes no sense for AWS to launch old instance generations in a new region. Also what do you mean by 10x more if you were using t2? t3 is available in Stockholm and cheaper than t2 (and t3 in Ireland).
If you were running your databases on T2 instances on regions supporting it, migrating to the cheapest available RDS instance type in eu-north-1 would cost $0.374/hr on-demand. That's over 9 times more than the price of db.t2.micro in eu-west-1.
https://aws.amazon.com/rds/postgresql/pricing/ https://aws.amazon.com/rds/mysql/pricing/
If you were running your databases on T2 instances on regions supporting it, migrating to the cheapest available RDS instance type in eu-north-1 would cost $0.374/hr on-demand. That's over 9 times more than the price of db.t2.micro in eu-west-1.