You are probably in the $1 - $1.50 per square foot range if I had togive a price without seeing the many complicating factors such asaccess, roof pitch, trusses vs stick framed, etc.
A few things I wouldstrongly suggest considering.
- Air sealing your ceiling is way more important than adding insulation.Do NOT even consider adding insulation without air sealing first. Onceall the insulation is removed this should be easily accomplished andwill not add a significant amount to the price of the of the job andyour payback on this portion of the work will be very quick.
- As part of your air sealing package, pay close attention to your atticaccess hatch/pull down stair. This is often overlooked. It's very importantthat this is well insulated and sealed properly or all of yourinsulation work will be wasted.
Also, I would consider blown-in insulation rather than rolledinsulation. There are pros and cons of each, but the rolled typicallygoes between the ceiling joist and creates a lot of gaps permittingthermal bridging.
- The blown in will typically cover the ceiling joistslessening the chance of thermal bridging through your framing members.
- Be sure proper baffles are installed at the eaves to prevent the windfrom blowing around your insulation.
Lastly, in your climate zone, the minimum code R-Value I think is R-30. It will be pennies more to blow in a few extra inches to get R-38.
For more information:
Read "What is the safest and most effective insulation for our attic crawl space?" a Q&A answered by Ian MacLeod.