Estimating Rehab Costs - Quick Formulas?

[Ben Valentin]

I know the best answer - "Read 'The Book on Estimating Rehab Costs' by J. Scott". I promise I will read it, I just haven't been able to purchase it yet. 

Other than that, are there any quick rehab methods out there? I've heard some say estimate $8-$10 per square foot, and I've heard others say $20-$60 per square foot. Are any of these formulas valid?

I have zero background in construction or rehabs. I'm looking into both rehabbing and wholesaling, but I know I won't always have the chance to have a contractor come in and do the bids or estimates BEFORE I make an offer to the seller. 

I want to go the route that some of these guys are saying and just get a deal under contract, but rehab costs are the biggest thing holding me back from making offers. Comps, sure. I can market and I can negotiate. I just have no experience with construction. 

I appreciate any advice!