You can get it for around 9$ on steam:
https://store.steampowered.com/app/363890/RPG_Maker_MV/
Usually it costs around the same as a AAA title. But it's cheaper right now because a game making contest is going on, hosted by publishers of RPG Maker. (And they use this as an incentive to encourage people to buy the game engine, and participate in the contest.)
It's a one time thing.
They make more money by releasing assets in the form of DLC, that you can buy & use in your projects. (Music, animations & graphics.)
They also have a free trial version on their website.
http://www.rpgmakerweb.com/products/programs/rpg-maker-mv