@Abe Macias what is the stabilized value for the project? The other commenter are certainly correct the cash flow analysis is not attractive--as you framed it above, but there may be value creation available from the build and in the land zoning.
For example, if the stabilized value of the duplex is, say, $460,000 and your total project cost ends up being $360,000, your gross developer profit would be $100,000.
For gross rents, again $2,200 ($1,100 x 2) would be a negative cash flow when subtracting $104 for vacant and assuming a 30% expense ratio with 80% leverage @ 4% interest and 30 year amortization, but have your checked the zoning? Is it possible to construct multiple structures or construct a 4 unit?
Another point in gross rents, I would double check the trends on rent increases in the market over the past three months 12 months and three years. Because inflation is so high and if, as you say, the local market is supply constrained then the rent increases in the local market could be fairly substantial. For example a 10% increase year over year on $2200 would be $220 extra dollars annually. Since it would take 12 to 36 months to build the property anyway you might be able to get a lender to finance based off of the pro forma value of the after completed duplex at a substantial rent premium to whatever your underwriting today.
As mentioned about $96 psf cost to build seems wildly low considering the market supply issues on materials and inflated demand do to low cost of capital and now congressional fiscal stimulus and tax programs.
Lastly, since you own the parcel next-door you might be able to get a blanket commercial mortgage finance them together based off of the income-based valuation that might be a scenario that is worth modeling out.
Best of luck sir.