@William A. - I use the rent multiplier rule all the time to gauge potential buy and holds in Louisville. It's harder when you're a little unsure of the rents an area can bring but you can do your research on Zillow and Craigslist (Map View) to see what the going rate is.
The following is better advice for Louisville and probably does not apply at all to high-value, high-appreciation tier 1 cities:
I personally would never buy a rental property where the monthly rent was less than 1% of the price + repairs / hardening unless there was something else at play... like it was a really nice house/area and I wanted to live in half of the property for a while. (I lived in two duplexes and turned one of my residences into a duplex as I was building my portfolio and those were mostly 1% deals) If however you think the appreciation on that property will be far faster/higher than others expect then it might be worth a leaner deal at 1%, but appreciation plays are mostly speculation/gambling.
If you're a doctor or high-income, hands off individual, than by all means, buy really nice 1% deals in nice-to-trophy areas and let appreciation and equity-build-up take care of you. That's what I'd do too! If however you're looking to move into rentals-as-retirement sooner than later, you need some cash flowing properties.
Your financing terms can make a 1% deal cash flow nicely. That is, you can buy a 150K duplex that rents (in total) for $1,500 a month if it's financed on fixed terms over 30 years. If however all you can get is 10, 15 or 20 year financing (and NOT at fixed rates) then the math is very different. You can only get so many conventional, 30-yr fixed loans, so I'd encourage you to use them for your biggest deals. After a time and a certain amount of rental properties you'll only be able to get commercial loans and it becomes a lot more expensive each month for the mortgage.
In Louisville, for strictly rentals, I'm looking for 1.2% to 1.6% deals. If you want to go to the west end (say 40th street and further west... the "best of the west" in Louisville) then you should be looking for 2% deals.
For comparison/reference, my last four deals... price+repairs in Shelby Park of 63K, rents for $829 section 8 (I'll fix this up and move it to a market-rate rental of $1,100+ when current tenants leave). Price+repairs in Shelby Park of 80K, rents market rate for $1,050, Price+repairs in Shawnee of 42K, rents market rate for $850. Price+repairs of 40K in N.E. Portland neighborhood, rents market rate for $800. (Portland is for the brave or foolish)
Best,
- Chuck