I serious doubt that you will find an accurate statistic anywhere:
If YOU had just finished your project, where would post it and why would you?
Something like this is not a matter of Public Record.
Most of the Renovations are done without a Building Permit.
Not to mention that every house is different and every project is different.
You will need to talk to a Contractor to get some perspective on YOUR PROJECT.
Good luck and may God bless... more