Builder here. Without walking round it nobody can give you a real figure, but this is how I'd break it down for a full gut on a 4-bed terrace with a mid-range finish and no layout changes. These are very rough guides and prices vary a lot by area and spec:
- Full rewire: £6k to £9k
- New heating and plumbing with a new boiler and radiators: £8k to £12k
- Replastering throughout: £8k to £12k
- Kitchen, fitted, mid-range: £15k to £25k
- Bathroom: £8k to £12k
- Windows, if they need doing: £8k to £12k
- Flooring, doors, skirting and decorating: £10k to £15k
- Skips, making good and the bits nobody budgets for: £5k or so
That lands somewhere around £70k to £110k before anything structural, the garden or moving walls about. Then add 10 to 15% contingency, because old houses always hide something once you start stripping out.
The one I'd look at hardest before bidding is that attic. If the staining is from a roof leak or failed felt, a full re-roof on a terrace can add £10k to £15k on its own. If it's condensation, it could be much cheaper (ventilation and insulation). The same goes for damp at ground level, which can be anything from a blocked gutter to replacing floors.
With sealed bids, if you can get a builder to walk round with you on a second viewing, it's well worth it, and a Level 3 survey once your bid is accepted will tell you what you're really dealing with before you're committed.
Making somewhere completely yours after a rough time is a lovely thing to do. Just go in with a contingency so it stays exciting rather than stressful.