Shit, is that how much a loft conversion costs these days?
I was thinking about half that. But I just want stairs, skylights, insulation and fairly basic finishing, not high end fittings or a bathroom or dormer.
I suppose for the OP, it depends what the cost of moving to a bigger house is, which could well be a lot more, plus what you're gaining, eg would the new bathroom be a second bathroom (good) or a 4th one (you already have more than anyone could really want/need). Plus any detriment, eg loss of a useful bedroom to make way for the stairs?
Although I know someone who's just done this and they've turned the box room into a home office and have gone from 2 bed and a box room to three decent sized bedrooms, extra shower room and home office.