In cities rent is easily calculated at purchase price divided by 1000 (drop three zeroes). If you hold a property long enough you will increase rent so it abides to 11 sec rule. To purchase properties that abide to the 11 sec rule you need to find cheaper propertie in the country. Read the book by Steve McKnight. Trick is to ensure rent is regular and property is accessible to your base location. Some commercial properties are more suitable and come with long leases.
But first read the book.

H Chalmer