What would it cost to use MonoGame for commercial use ?

Nothing… it is free to use for any game.

While XNAandMonoGame are free, you still have to pay to put your games on platforms. Steam is $100. You may also have to pay for development kits on PS4, XB1, Wii U, which I’m guessing is around $1,000-5,000. Certain platforms also require

So i can publish it and make money and don’t have to pay ? i will only have to pay for the stores and for some development kits ? I have a paid xamarin account will that help ?

MonoGame itself is completely free, no royalties.