Government spending at its finest, general incompetence from people that don't know or care about how much things cost while "experts" throw increased costs at them for personal interests, often while having a very low understanding of how much money things need.
I've been watching local contractors absolutely fleece the local councils for years, they'll hire a million people for stupid things but they wont hire or screen anyone actually from the working class to advise on the things they do, and then should anyone dare ask they'll claim there's a billion different reasons as to why things cost ten times as much as they should have. When anyone asks, they'll appeal to (supposed) authority while bob the builder quotes them nonsense numbers because they know they'll agree to it.
I'm not disputing that bats might well need saving, or that having a design like that might help, I'm saying it shouldn't cost anywhere near that. The reason it does, and half the reason we have horrendous costs for any public projects, is because those in charge have absolutely no-blumming-idea about how much projects really cost so they get fleeced to hell and back. There's no communication because everyone is trying to rip off everyone else, what a time to be alive!