I did some more research today on property taxes for the Tulsa property I am buying. My original estimate for taxes was $371 per year, which is what the current owner is paying. Turns out, that figure is because the owner was able to buy the house so cheap. From what I can see on the Tulsa County Assessor's website, property taxes are calculated based on the purchase price (for new home owners) and the school district the property is located in. This property is located in the T-1A school district. Based on their Tax Estimate Calculator, my taxes will be about $1,000 per year. That's almost three times the current tax bill!
Using this new figure, it looks like my cashflow will be around $140 per month instead of $200 and my ROI will drop to the 16% range. This is assuming a standard loan amortized over 30 years. If I use an interest only loan, I can increase the cash flow by about $60 a month, which gets me back to my original numbers. However, I am very leery of interest only loans, so I'm not sure I will go this route.