Government spending always lists the top price but it never actually costs the government that.
They spend £3bn with companies like BAE for weapons. BAE pay tax on profits - and employ people. Those people pay tax in their salaries and spend money. They pay tax when they spend it.
By the time the money has flushed through the system, the net cost to the government is never anywher near the £3bn initially spent. Same with lots of other spending announcements.
Or we could not spend that money, damage relationships with NATO, especially relationships with the EU and the US and let Putin do WTF he likes.
Seems like good value, to me.