Gungrave G.O.R.E

There are a total of 9 demo shots that you will need to acquire. I would recommend saving this for last as in my experience the variety isn't really needed. YMMV but I really only used the default demo shot (to grind towards 500 activations), Raging Inferno (clears crowds in an AOE), Death Sentence (Boss fights) and Seed Fall (Wipes out any enemy in the game that is within a line in front of you).

1. Blood Rain - Your coffin, Death Hauler, launches multiple mini-rockets.
2. Death Drive - Death Hauler is split into two large swords that you use to slice and dice.
3. Death Sentence - The coffin transforms into a laser gun that can fire in all directions.
4. Doom's Rain - The coffin launches six homing missiles at enemies.
5. Graveyard - This is a special ability that slows down enemies' movement.
6. Hellbound - The coffin becomes a minigun that fires large-caliber rounds.
7. Hellfire - Death Hauler becomes a flamethrower.
8. Raging Inferno - Use a combination of the coffin to hit enemies near you and guns to shoot at them.
9. Seed Fall - Your coffin becomes a cannon that fires a round that pierces through enemies.

If I did my math right all of these should cost you about 40,500 DNA which will come around either the end of your second playthrough or about halfway through your 3rd depending on what rankings you've been earning. Alternatively you could also grind "No Man's Gate Revisited" if you have no intention of going through this game 3 times.