In the span of 5+ decades, the galaxy witnessed the completion of construction for at least 3 planet-destroying superweapons: Two Death Stars and Starkiller Base, each one several orders larger and more powerful than the last.
Their construction are massive operations with massive labour and resource costs, yet somehow the galactic economy didn't seem too dented by their construction (in how resources are siphoned off in secret) nor destruction (in how the news could have rocked Imperial economy), in the sense that poverty and economic woes were never mentioned as the primary reasons for revolt and rebellion against the Empire.
Even the First Order, who inherited the terms of the Galactic Concordance, could somehow afford Starkiller Base, a brand new fleet and a new army of stormtroopers (apparently superior to the Palpatine era version in training).
So how easy is it for the galaxy to afford and build a planet destroying superweapon? We know the cost isn't negligible, since Death Star I was already expensive enough to compromise on the Imperial Navy's budget, which some officers felt would have been a better use of credits towards crushing the Rebellion.