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We paid £65k all in for a end of terrace conversion last year. I think you'd probably pay two-thirds of that if you can find a builder to do what you want.
I do think what you are asking for is unrealistic though - if you want it insulated (and you will have to in order to meet building regs at some point), then you'd need to do the first fix for the electrics and plumbing. What's driving the idea of doing it partially, budget presumably?
Sorry, another vague question. How much do you think it would cost just to do the structural elements of a loft conversion? For now, I just want to create the bare bones of the the space. No boarding, heating, electricity. I have a Victorian terrace house.