This might be slightly off topic, but it seems pretty hard to find any properties that sell for $150k and rent for $1900 which Jake posted as a quick rule of thumb.
So while I think the 50% rule is a good quick and dirty approximation. I think in practice its pretty bad for some single family homes. I'm similar to the OP here in that I'm looking for relatively easy to rent, newer properties and I'm out of state so I won't be managing them myself.
I'm up to 11 rentals, but only started since 2008. Mine are all roughly in the same price range as OP from 100-175k, but consistently the expense ratio (excluding financing) is usually more like 30-35% of rent, with the only estimated components being repairs (I budget a fixed $600/year per property, and I use a vacancy rate of 4%) But including taxes, hoa, property mgmt, vacancy, repairs, insurance, advertising costs for turnover all the properties are in this narrow range.
I know my NOI targets tend to be less agressive than full time RE investors, but I'm pretty happy with properties that hit close to 7% cap rate. Usually that gives me roughly a true 10% cash flow return on actual upfront costs (repairs, downpayment, closing costs) since mortgage rates are so cheap and less than the cap rate.
My view on this is I'd rather pay a premium and take lesser cash flow up front, for properties that are easy to rent, newer and require less repairs(less work/headaches), and if there ever is appreciation, these should do better than the lower end properties...
Especially given that OP has a stable job, and limited time, I don't think its realistic for her to expect to get primo deals as well. I would recommend factoring in repairs and all the other true costs of ownership to figure out what the true estimated cash flow would be, altho discounting rent heavily might offset some of that.