Updated: Oct 27, 2018
Zulrah may look hard, but once you know how it works, it's actually one of the easiest, safest bosses in the game. It has far lower requirements than Vorkath, and you'll only need 80 Magic and Range, and a decent Defence level in order to kill him.
Of course, you'll need Protection Prayers as well. In order to get to Zulrah, you'll need to have started the Regicide Quest, and you can use a Fairy Ring plus an agility shortcut to get here, but I would recommend using the Zul-Andra Teleport, but only once you know you'll have a guaranteed kill at Zulrah.
My whole gear setup right now is about 2 mil. My Trident is only about 100k because I only charged it with 200 charges, and the rest of my gear isn't worth that much at all. So, you can do Zulrah with not a lot of money, and make millions per hour. Elite Void works very well at Zulrah, but void Mage is not all that good. You'd be better off taking Ahrim's and Karil's, or Armadyl, but for the sake of this, I'm showing it with black D'hide and mystics. The best weapon to use at Zulrah is the Twisted Bow. But the toxic blowpipe, or an Armadyl or Dragon Crossbow will also work very well. The Trident of the Swamp is very recommended, but it can super easily be done with the Trident of the Seas as well. You will definitely need an Antivenom, and you'll also need Rings of Recoil.
At the end, I've linked a picture which I'm using, and I always use when I kill Zulrah. What this is is the 4 different process that Zulrah can take. By the third rotation, you'll know exactly which process it is, Alfa, Bravo, Charlie or Delta, and all you have to do is just kind of keep one ahead at all times. So, always know where he's going to go next, and what prayer you'll need, and then just check again once you've moved to the next place. On his ranged form you need to prayer range and use Magic, and on his Magic form you prayer Magic and use Range. He has a Melee form as well, where you do not need to use any Prayers as long as you're standing in the safe areas, and you should be using Magic when he's in his Melee form. Zulrah also has a Ranged form that is similar to Jad. However, he always goes from Range to Mage, then range, then Mage, so you always know what he's going to do next.
When you get to the Jad form, watch his head, and watch when it bobs down. Each time his head bobs down, you should switch to the opposite Prayer to what he's using. You can see here it's so easy to avoid all of the damage from his Jad phase, just by watching his head, and flicking prayers each time. At a lower combat level it's possible to get over 2mil per hour at Zulrah, and at higher levels if you're getting 2min kills, you can get up to 4mil an hour. Currently, the blowpipe is almost 6mil, which is one of the key things that makes Zulrah so profitable right now. Throughout the fight you should always be aware of your Ring of Recoil and when it breaks, because once it breaks you'll take a lot of damage from the little snakes that are around. They only have 1 health each, but they can hit very high. So, once your Ring of Recoil breaks, make sure you put on another one straight away. As you do more and more Zulrah, you can gradually upgrade your gear as you go. With each upgrade, your kills will speed up by a little bit.
Zulrah Cheatsheet: https://i.redd.it/2g6oirse2wny.jpg