A 2400 square foot duplex (1200 square feet per unit) at roughly $150 per sq ft to build = $360K  So, roughly $790K all in.We estimate we can rent these brand new units for about $2500/month, grossing $5000/month.We're not sure what the property will appraise for when done, but if we refi once it's done (BRRR) and pull $700K out, it looks like the mortgage payment + taxes & insurance would be about $4000/mo.  

In most cases the bank will want 20% down so your mortgage will be around $280k and over 20 years thats around $1800 a month off the top of my head. plus account for a 6% vacancy rate and $2400 a year in repairs and calculate how much the HOA fees are and insurance and the real estate taxes.

You will need insurance in the name of the partnership (LLC) and it sounds like this is a new partnership so anybody that owns more than 20% will have to personally guarantee any bank loan.

My question is, why is the insurance so darn expensive?

my guess would be water,sewer,taxes,insurance, maintenance, capital expenditures, common areas (everything but the principal +interest ) 

The tenant (or tenants) and their guarantors are responsible for ensuring it's mold free as it was when they moved in.Is there Tenant insurance?

Sure, insurance may help, but the population changes immensely.

I am slowly paying down one that requires flood insurance in case the insurance gets ridiculous, but other than that, I'm happy locking in what I have now.        

I looked as stocks, realestate, gold, insurance, etc...

Meghan,I insure several 2 unit Condo Associations.