Goes great with bury the dead

Thank you for pointing me that direction, I found the mod maker for that mod talking about how they managed that on the nexus upload and got the costs how I want them. For anyone else's reference, you have to edit fcs.def and find the relevant cost, then change whatever line defines the options for what you want to put a weird cost into.

The reverse engineering mod found a way to make a weapon be the cost of researching a tech, perhaps that would help you figure out making a weapon the cost of the building.