They are not too expensive. Those Guilds are to cheap on leveling up Treasury Great Buildings.That the members decline or refuse to level up their own Treasury GBs is their problem, and the Guilds leaders problem for not knowing or caring to force the Guildies to level up Treasury Buildings. The fact is everyone in the cheapskate Guilds thinks someone else should be helping the Guild Treasury, and they all have excuses why they don't. (this has been true since I started playing Foe!!)
Lucky for me all three of my Guilds are concentrating on getting everyone to level up Treasury GBs. And the reports from Guildies watching the Treasury is we are doing a great job! And we all will keep at it until there is no longer any issue on making as many GbG buildings as we desire!. And that is the solution. Not whining that they can't build them because they 'cost too much".