Hard to know but with trades doing the work and current lack of availability of trades in the SE.... £120k minimum.
Damp, fundamentals will all need doing ie wiring, heating, roof, flooring, garden landscaping and possible knotweed and vermin remediation, structural works quite probably, stripping back to brickwork and plastering, decoration, and finishes (ie kitchen, bathroom, flooring) No chain may mean unmortgageable or otherwise problematic from a legal POV - I.e. unlawfully converted into separate units, unlawful modifications, absent planning or building regs. Would not touch with a barge pole.