How do I bathroom / kitchen / extension? etc.

Guessing a lot of the areas where you might have saved proper money would leave it noncompliant with regs.

The biggest saving would seem to be in the build rather than the finish, figures for just builds seem to vary anywhere from 50 to 100k.

Our build was around 60k and unless the builders are doing something that is really specialised I can't see where the extra 30k would go (even with different cladding options)?

We've pretty much finished the loft now, I was meaning to put a full breakdown of costs on here if it would be useful, as I was completely clueless with regards to costs before we started and I'm sure I'm not the only one?

I suspect this might be less costly- Or not- I was just impressed by it.
https://moduloft.co.uk/
Also- unrelated but there is a deaf contractors doing work down our street, and I have genuinely never seen any set of builders work more efficiently.
They're called EGL- but I can't seem to find the details, I'd like to find them to save them for a later date- if anyone with better google-fu can help.

Yello ! I’m massively hungover. raw finish / exposed stuff - maybe - but it probably has to be pretty agricultural to save real money. - It’s a fine line to get to something doesn’t look like a squat and also saves money. What’s that thing ….? - good, cheap, quick - pick two. With steel it needs paint fire coating to be exposed - extra design money to make sure it looks good in the space too. If you mean trendy exposed timber roof rafter/beams - that’s a no go for your loft because you’ll need insulation between and under to meet thermal regs. References.

Just go bog standard loft company box, whatever cladding, windows, electrics, etc is cheapest.

Unless you're not working then paying pros to do it at the time is going to be cheaper than the cost of your time.

Loft companies throw up loads of lofts, if you're flexible and go with their easy route that's going to be the cheap option.