To get infinite money, you need at least $45, 000 in in-game money.
Once you have that – go to settings and press ‘restart rebirth 1’.
While you are in the game tutorial, pause – then press ‘character’.
Now go to the infinity blade.
Now ‘master it’ using the money mentioned above (where it shows the item’s xp look to the far right of the xp then press the arrow).
Now you are able to sell it (you might need a good weapon to finish the tutorial), now finish the tutorial and start rebirth 1.
Pause again and restart to rebirth 1 (repeat the process as told above but you won’t have to master it again).
Keep selling the infinity blade and you’ll be rich (this also works with the other items)!