I've heard that argument before. "MTG isn't expensive! You can build a good deck out of commons and uncommons!"
Its not a argument, its a fact - its easy to play the system to the point where you dont even need to pay a single penny.
Like for an example, this draw I just made just a min ago - costed me only 25 mythrils - you get one mythril for each battle, each day you can get 3-5 mythrils for free just by logging in, and doing special events such as anniversary events, you can get 25-50 per run.
There's no point in paying anything - people who pay are people who have no patience or self control lol.