Crystal Slayer
To get a crystal slayer task use ::crystal or the Teleport -> Dungeons -> Crystal Caves and talk to Elf Tracker. Tasks cost 5m/GP each.
A good way to slow the depletion of your cash supply is to high-alch all decent drops, vote twice a day, and do Seren each spawn. This should hopefully somewhat balance out the GP flow.
You can only kill these monsters on-task and have a chance of receiving Crystal ores, Crystal Helm, Body, Legs, and an enhanced crystalline key which is used to fight Hunllef.
You can use a Dwarf multicannon in the caves which does speed up tasks significantly, however at the cost of cannonballs.
Each armour piece costs 7500 crystal ore to be upgraded to full Corrupted (perfected) which is best-in-slot range gear.
The Bow of faerdhinen costs 15,000 ores to upgrade.
Another way to receive crystal ores is via killing Hunllef where you will receive 150 ores per kill, and have a chance to receive some from the Hunllef chest.
To use your enhanced crystalline keys head to Teleport -> Bosses -> Hunllef
Be sure to read the Hunllef guide.

See below for monster and agility shortcut locations.

| Crystal Ores per kill | |
|---|---|
| Bat | 1-5 ores/ kill |
| Spider | 1-5 ores/ kill |
| Unicorn | 1-5 ores/ kill |
| Rat | 1-5 ores/ kill |
| Wolf | 3-10 ores/ kill |
| Scorpion | 3-10 ores/ kill |
| Bear | 4-15 ores/ kill |
| Dark Beast | 4-15 ores/ kill |
| Dragon | 4-15 ores/ kill |