Or $0, if you use the Starter edition. It's free for hobbyists, students, startups etc, with the clause that if you start making over a certain amount of revenue you're asked to buy it.
but it seems and correct me if i am wrong
you cannot use the starter edition to create an application that connects to a database
which in my opinion makes it useless, RAD tools are mostly used to create line of business applications
..which blocks off a lot of arbitrary features, including iOS, OSX, UWP, and 64 bit compilation of all things.