This achievement is no different than "Red Orb Millionaire", as you only need to collect about 1.75M for all items.
You DO NOT need to buy Holy Water's just everything else, including all blue/purple/gold orbs.
Taken from my Red Orb Millionaire guide:
Requirements/Optional:
Devil Trigger(The better combo done to the red crystal the more orbs you get)
Super Costumes (Same as Above)
Bought Trigger Heart (Allows DT to last longer)
Bought Max-Act(Very handy for doing more damage for more orbs)
Bought Most of the Red Queen Combos(Self Explanatory)
Notes:
I would advise doing this then going after all items.
I would also advise to do this BEFORE "Dante Must Die" mode, as DMD mode is VERY hard and is MUCH easier with items, and it would be a huge waste to use items before you get the achievement.
Guide:
1. Simply start Mission 3.
2. Follow the train track to the left.
3. When the camera changes, go south.
4. Camera should change again & you should see the Red Crystal behind a fence-like thing.
5. Destroy the fence then let loose on the crystal.
Best to use DT mode while raping the "Max-Act" button (Usually LT).
6. Once the crystal is destroyed, go to the start menu then "Systems -> Retry Mission"
7. Repeat.
You should get about 3000-8000orbs per 20-40seconds.