Counting the inevitable enormous muck-up that results in me having to build it again from scratch?

A lot. Most of that will go into batteries and having the bar cut I reckon. The hardox for the main body won't be too expensive I'd imagine and the bulkheads are just mild steel box section which shouldn't be too expensive either. It'll definitely cost more than HardWired 2 did, but as of now I really don't know given that I haven't finalised the parts yet...