I have a property I converted to a rental from personal use. How do I assess how much I paid for it at the time I started using it for business? Where do I find the FMV?

I bought a house in 2017, lived in it, then rented it out for part of 2018. How do I calculate the Cost (how much you've paid for it, including whatever you spent to acquire it at the time you started using it for business)? Where would I find the Fair Market Value in case this is the lessor of the two?