There isn't 1 definite answer, since slayer is SO diverse. You could buy bandos and wreck tasks like Scarabites, but would that be so useful at Mutated Bloodvelds, where you need to constantly pray melee? You could buy a whip and have smooth sailing through most tasks, but would that be so useful at Waterfiends, where you need to use crush to be effective? You could buy a Godsword, and deal high damage (if not less effective than the whip), but would that be so useful at Wyverns, where you need to use an elemental, mind, or dragonfire shield? You could buy a Dragonfire shield, and get through most tasks easily, but would that be so useful at Kalphites, where you really don't need the defense? So if money was no issue (but not considering really expensive equipment such as Spirit Shields), the best equipment would be: -Whip -Dragonfire, but also with a Rune defender for locations where the defense isn't need or isn't helpful, and a Zamorak Book for ranging -Fury -Barrows Gloves -Slayer Helm, of course -Zamorak Spear, fastest way to kill metals and Aquanites -Saradomin Sword, fastest way to kill Gargolyes and Waterfiends -Bandos armor, with Prossy for tasks where you must pray -Cannon with cannonballs -Void or Armadyl, for tasks such as Black Demons where you safespot + cannon -Saradomin Godsword, but also a Dragon Dagger or Armadyl Godsword for tasks where you don't need the extra healing -Dragon Boots -Berserker Ring (i), but also Warrior Ring (i) where you need attack more than strength, and Onyx Ring (i) where you need attack more than strength and you aren't using Slash (ex. waterfiends or mithril dragons), also a Seers' (i) for tasks where you range + cannon. Of course, for practicality you could forget the Warrior and Seers (i) and just use a Berserker and Onyx -Unicorn for healing, Elemental Titan when you want healing and fighting, and Steel Titan just for fighting -Karils -Rune crossbow with Broad/or better, bolts -Knives, for range + cannon fire giants -Chinchompas, for Nech tasks. Ice barrage is an alternative, but not a very good one. -Overload Potions, plus Extreme Antifires and Extreme Prayer -Praying piety on all tasks Of course, in your 13m budget, you would need to pick and choose which ones you think are the most effective, what master as you using? On Barrows, it does add up, but not to much. If you really think about it, you only pay ~15k per hour to use a barrows top and bottom. You can easily afford that.