I currently have a 3/1, approximately 1300 square foot under contract. 

The home foundation appears solid and only the deck supports have settled due to insufficient footings. 

Keep the supports, footings, joist the way they are and just replace the deck boards, railings.

Is it per square foot?

If you look at median sold price per square foot of resale sfr it actually has gone up for April compared to March. 

When I divided the price by square from from realtor.com it came down to $504 per square foot-Offer: 300k at 3.75 for 40 years =579k after interest and principal.

It was my first investment and I wanted a low stress property to get my foot wet.

It's a 1200 square foot Bungalow in the northern suburbs of Detroit. 

Unfortunately during my due diligence phase, I learned the maximum square footage allowed on this lot is 2400 sqft (including the garage). 7900 square foot lot, 30% max or 2400 sqft, whichever is greater.

And he is claiming net rev 200k . 1500 square foot.