As mentioned, from the monthly rent you'd subtract out current monthly dues, and maybe a management fee. 

I typically subtract 3%, of the ARV.Realtor Fees: What is the commission you are willing to pay your listing agent (unless you are the listing agent) and the buyer's agent.

Subtract that from your price/square foot number. 

You can also subtract financing costs from the NOI to determine your cashflow, ROI and ROE.

@Zach Shuler - the "50% rule" is to take the monthly income, subtract 50% to estimate expenses, then subtract your monthly mortgage payment.

Then subtract off your repair costs.

I agree about subtracting insurance + property tax + maintenance but 50% rule seems to be crude.

I typically subtract 3%, of the ARV.Realtor Fees: What is the commission you are willing to pay your listing agent (unless you are the listing agent) and the buyer's agent.

To do that figure the payment on a FI calculator and enter that as your payment, take the loan amount and subtract all costs in getting the loan and enter that as the PV, enter the loan term as N and then solve for I the interest.

You would lease-option the house for $100,000 from the Seller and then assign the deal for $5000.The assignment fee is generally subtracted from the purchase price, not a deposit or down payment.