This achievement may sound daunting at first, but is in fact quite easy. As you work your way through the various difficulties, you'll earn red orbs. You can obtain these by killing enemies, killing Lost Souls, destroying red pods and by killing spiders.
You can get this achievement while working on the achievements for upgrading Dante's Health and Devil Trigger completely, as you'll need to buy several cross pieces to get those. The final ones you can buy in the store are both 10.000 red orbs; two flies for the price of one!
Spending 50.000 Red Orbs will earn you the achievement "Absolutely Crazy About It".