The party that I'm the DM for recently got use of an airship, which came with a ballista and harpoon. The first thing that one of the party members wanted to do was purchase even more siege weapons to use on it. Well, that's fine, and it's helpful to find something for the characters do with with all that wealth they have walking around.
However, while the DMG lists several siege weapons and how much damage they can do, there isn't any indication of how much they might cost, how long it might take to have them built, or how much they weigh. I can certainly just make up some numbers, but it'd be really helpful to have a starting point. Is there any standard recommendations for weight, cost, and lead time for siege weapons? Maybe something listed in some other published adventure, or based on similar items elsewhere?
If setting matters, this is part of a Storm King's Thunder campaign in the Forgotten Realms.