The PFM-100 Hydrazine Torch Flamethrower costs 11,000 credits. This will come naturally over game progression if you just stick to that weapon. To kill them faster obviously go for the limbs first as mentioned in the game. Otherwise you just wasting ammo. Especially for this kind of weapon. If you're going for this tropy better ONLY HAVE THIS EQUIPPED in order to get the same ammo back from fallen enemies.