have a look at this:
Casa Metti
the property was bought for €20.000 and the restoration costs, including all professional fees, water, gas and electricity connections, best of materials, were of €120.000.
I would say you should think of a cost of about €1600 per sqm for renovation. Of course it depends on the levels of quality you would like to achieve...
Get an Architect, get yourself drawings and specs then interview a few firms and compare prices...
Paola