You are exactly right. FMV is the the market sale value of the property for calculating depreciation, not the monthly market rent.
When you convert a property from personal use to a rental the property's Fair Market Value is the amount a willing buyer would pay and a willing seller would accept when neither is compelled to buy or sell - an "arm's length" transaction.
If you need an estimate of Fair Market Value for your property, check with a local Realtor (best choice) or look up similar properties in your area on Zillow.com (may be inflated). The lower value would probably be a good choice.
