A very rough rule of thumb is 1 % of the value of the property as an annual flood insurance premium. (themultifamilyguy.com)
The really rough rule of thumb that I use is that what I pay for a property is equal to just putting that money in savings and drawing off of it for 30 years. (biggerpockets.com)
A (very) rough rule of thumb is to save 25 % of your gross paycheck. (retailinvestor.org)