Unfortunately your question is of the "how long is a piece of string" variety. You need to have an experienced building contractor / architect / surveyor walk through and inspect the property and draft and cost a schedule of works, IMO probably also to include rewiring, re-plumbing and re-glazing.
You have encountered the perpetual property developer's dilemma :-
Is Total Purchase Cost + Refurbishment Cost >= Completed Value?
and
Is Total Purchase Cost + Refurbishment Cost <= My Budget?
If the answer to either question is no, then developers will look for an alternative property.
Banks are no longer likely to fund this kind of speculative undertaking so unless you have access to funding apart from the mortgage, you probably need to look for another property.
Unfortunately a property and a price for it are only "perfect" if they fit within your budget, otherwise they are just pipe-dreams.