Hate to be a pessimist but here's my 2 cents for what it's worth...
Not sure about the Sq. Ft. cost as I usually operate in metres, but for a new build I would generally advise people that 1500euro per Sq.m. would do a nice, but plain job (no stone counter tops, no hardwood floors sort of thing) and 2000 - 2500 per Sq.m. would finish things very nicely.
Don't forget this is the average cost across the house, obviously some rooms are going to be cheaper than others, but considering that a good kitchen including appliances and nice units & counter tops can very easily stretch to 20,000 and hardwood floors for a typical ground floor to around 5000, not to mention windows - any sort of nice large ope timber framed window can cost thousands too, fireplaces, light fittings, cost of an electrician, plumber etc. Are you going to go for under floor heating seeing as you're new-building etc. Bathrooms - good taps can be 300 - 1000 a piece, tiles etc.
EVERYBODY under budgets when building - I generally try and advise a higher cost per sq.m. initially, if you save - great and if something comes up then you'll have a bit of padding - for example during the build of a house they struck upon an under ground river - the foundations had to be re-designed, there was a 2 month delay and the whole process cost 25,000 extra - and you haven't even gotten out of the ground yet!
Don't make the mistake of under-estimating your budget.
Good luck.