Preventivo

How long is a piece of string? As regards a septic tank, I reckon it should be possible for less tan 2K. I put one in recently, (but did most of the work myself - except the digging!) for around 1450 Euro in total.  I suggest you should get more than one estimate for the works, but of course it's difficult to know you are getting genuine quotes and not being diddled by colluding builders.. Buona Fortuna!!!

Just had a quote for balony railings that wrap around two sides of the house at nearly 4000 euros although they are about 16 metres long in total plus one storey scala. this seems a lot. Anyone got an idea what we should be looking to pay per sq mtr?

I'd have said about €100/m for the balustrade, perhaps slightly less if it's straight forward

  We had a budget to hopefully get one floor finished but these prices blow it right out of the water and I would rather stop now than spend another heap of cash and still not be able to live in it through lack of habitabilita.

Sorry to hear that, the house will be very difficult  to sell in it's present state. A reliable UK builder who fancies a nice long holiday in Sicily would be nice - but then that might upset the locals.

I'm sorry you're finding the house unaffordable, but if your roof is 125 sq m and you have two floors, you (ball park figure) should have been looking at something like €1,500 X 250 = €375,000 as construction cost alone. If your avatar is a pic of the house you haven't stinted on balconies and terraces, which also have to be paid for, and then there are all the utilities costs to add on top, apart from the taxes and professional fees. I fear you may have fallen foul of the understandable temptation of 'a ruin', and than failed to ask the right questions all along the line when getting 'persuaded' into going for new build. It is the most expensive way of acquiring a house - considerably more costly than buying a new-build already finished.      

In Sicily you would pay 1500 psm finished to a high standard over and above the cost of the land.  There is no reason why you cant finish one floor and get abitabilita, but you might have to split the house into a villa bifamiliare to do it, and make sure that the floor you finish has all the requisites for abitabilita. HOwever, should you decide to sell, it is common to sell a rustico tamponato in Sicily, and wouldnt present problems.