Difficult to say exactly without knowing the current situation of the financing of the ground. The last accounts available are those to 31st May 2011, and the transfer in ground ownership back to GFC was after that. The 2012 accounts probably won't be available publicly until Feb / Mar 2013.
In the 2011 consolidated accounts (covering all PS companies relating to GFV) there was a net debt of about £13.5m, of which £10.1m was apparently a loan taken out against the ground, which was valued at £10.1m. So whatever deal was done to return teh ground to GFC will probably be significant in establishing the current actual debt of GFC.
I seem to remember somewhere PS saying that he would sell the club for £1 to the right person, but of course that person would take over responsibility for the debt. So assuming the situation isn't a great deal worse than reported in 2011, £14m should be the most you'd need to buy the club and pay off the debt.
Recent annual losses have been up to £500,000, so as a rough guide reckon on that as an annual excess of expenditure over income and you probably won't be disappointed.