I'm struggling to find an estimation for this renovation; would it be best to get in touch with a QS? or would the online estimator services provide quotations/ballpark figures for it?

 

I'm hoping to keep costs to around £2k/psqm - but have no idea how feasable this is what with prices rises across the board.

 

Approx GFA: 1800sq/ft

What a lovely old barn. I did a conversion and found it very difficult to get quotes because of the uncertainties. Have you had structural engineer's report as the condition of the foundations will markedly affect costs? The first SE I had, advocated underpinning, a second opinion deemed the foundations adequate. About £15-30k difference (the price of underpinning varied this much), but this was a much smaller building than yours. 

Wow...  demolish and re-build would be my first suggestion.  Assuming that's not an option, I'd try and get a reputable builder or two over for an informal chat to get an idea of how viable this is.

Without seeing the state of the roof timbers, £400k is a tidy budget and could be achievable. First stop would be a structural engineer, and someone who does decent modelling of what’s possible - consider a steel portal frame inside the existing building for example and keep the outer as a decorative shell. 
 

it’s not listed is it ..???

Thats a lovely old barn and the new design is very modern. I like it.

 

My advice would be to find a decent local small builder with great references to either price the structural work or do it on a cost + basis. There are so many unknowns in barns that people tend to go way over with their pricing 'just incase' 

Thanks all for useful comments - unfortunately looks like we were too slow and it's already been snapped up ☹️

Bad luck.