I'm sorry, but 500k-1m is NOT a small amount. That is all of my money. Not everyone has gil bleeding out their ears.
It IS a small amount. You can easily make 50k+ from gathering clusters per hour. And probably a similar rate from fishing.

As long as people need materia, then people will use crystals and clusters to craft the stuff you spiritbond. Also, people will buy foods and potions for Coil, and possibly for Crystal Tower, especially now that they won't expire on deaths. People on the fence about buying 15 foods because of 14 wipes, will now buy it because they'll only need 3 for their turn, the cost/benefit will be reasonable enough. If people want to become rich, they won't all stop spending. Because they need to spend on certain things to make certain other things. Not everyone gathers everything on their own.