hello is the warframe game on ps4 completely free?

As far as PS4 goes, I don't know since I play on PC. However, the game should be completely free to play; so once downloaded you should be able to enjoy Warframe at your leisure. Everything in the game is free and obtainable except for exclusive and event items. You don't have to pay for anything in this game. However, the only time you will want to use money is to buy Platinum (currency obtainable through $money$ purchase), and with Platinum you can use it to buy more Warframe inventory space so you can use more Warframes, Weapon inventory space, Sentinel inventory space, straight-out purchasing weapons and warframes without farming or waiting for crafting time, Super charging potatoes to allow more modding capacity, and rushing craftings.