Borders can remain open too. You need to spend resources from the budget to keep your borders closed.
Borders price is not set as a constant, it does change depending on the amount of currently opened regions. It increases by 0.1% every minute if there are more than 70% of regions with closed borders and lowers by the same amount if the number of regions with closed borders is less or equal to 70%.
All this can be regulated by passing the specific laws.
|Resources||Spendings (for 1 minute in 1 region)|
You can navigate to Maps and select a filter, which will show where the borders are closed and where they are opened.