Bath or kitchen? or both?
Carpet or hardwood?
Paint or wallpaper?
Like in the Last Samurai - too many minds/variables.
Look at properties that have been renovated which you like, talk to that contactor, and add 25%.
Also, go to town hall and view their permits for the costs of renovating.
That can be enlightening by itself.
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When I got into the industry in the early 90's I did 203K loans for real estate investors. Their cost per foot was around $90 for renovations. Prices have increased. Louis is correct the finish work is your option and will deternine ultimate cost. But a rule of thumb in MA use a minimum of a $150 a square foot to begin your estimate on a true gut renovation. Be careful the $150 is not for doing a kitchen or a bathroom -- it is for a full renovation as a base line for looking at property.
Get estimates on what you want to do -- always have a plan and see if it makes sense
Best of luck
Lets say a jeep grand cherokee, cloth seats, no nav, no sun roof, v-6 $30,000
Now you want the grand cherokee with leather, nav, sun roof, v-6
Now you want the grand cheokee Limited v-8 $42,000
Now you decide you want the grand cherokee overland package
Now you decide you want the grand cherokee SRT $64,000
Same goes for a house, from choice of windows, siding, kitchens, baths, lighting fixtures, appliances, contractors, architects.
So as you can see its based on your tastes, expectations and pocketbook.