Contractors: Average $/SF for additions in Suffolk Cnty, NY

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This is a question for any contractors or anyone who is good at estimating contracting work.

I'm getting close to starting on my first flip, but not without getting an accurate cost breakout on the additions and/or repairs needed.  Does anyone have a typical price per SF for rehabbing that they use when budgeting? I know that the costs will vary by property & repairs needed, and that I need a contractor or seasoned professional to look at the property to make a final determination, but I'm looking for a simple figure for analysis to help quickly weed out properties that aren't worth acquiring.  I'm particularly looking for figures such as $/SF for:

Building additions: 1 story + 2 story

Painting (Interior)

Lawn resodding

Patios

Decks

Also, are there any good sources for finding local construction/contracting/rehab figures? Thank you in advance.