Dragon Platelegs is great. Amulet of Glory is great. Ring of Wealth is good. Another runescape 3 gold cheap yet powerful alternative is the Explorers Rings. Obby cape is great. Dragon boots is good (if you get them) For your weapon I would definitely go for a whip and/or a Dragon Scimitar. Monkey Madness is required for the Dragon Scimmy plus it does take some time but it's definitely worth it for training Power. Whip on the other hand is excellent for attack and defence.
Dragon Defender is good (once you FINALLY get it). Additionally for a fantastic pair of gloves I recommend doing RFD to get Dragon/Barrows gloves. Heck even Mithril gloves are really excellent. To get them you need to perform Recipe for Disaster, and I definitely suggest that you do this to the maximum you can...
I find myself asking the identical question. Imo, slayer is no where near as good as it used to be (just looked what happened to the whips). Camping in abby demons for 75-125+ kills only for a 900k-1.5mil fall?? Now for a 3mil drop would differ. Slayer is an enjoyable way to train melee stats so if you anticipate doing coaching, go for it. Its a nice way to split the repetativeness of training on a single monster.
And the principal profit in slayer doesnt come in the big drops, its the small ones adding up over time along with clues if you do them and if you are smart herb runs involving jobs. Well your best, I dont have 85 slayer. There has been accounts of not obtaining a whip drop in 4-6 hours of continuous slaying. The simple fact of the matter is that the whip is an uncommon drop. Any help website you go to will record it as one.
The likelihood of obtaining a whip inside a 75-125 kill range is potential, maybe not tipacal, but possible. You've got more of a chance of getting it within a 1-540 kill array. However, you might not get one. Also, if you ask anybody why they instruct slayer, its almost always for the big drops. Ex: Saved from abby deamons, sol from ice strykewyrms etc, etc.. Even if they slay for all those drops most of the gain wont come from them, particularly on ice wyrms they have drops that are amazing, the SOL is just a little bonus. The 1/540 comes in the ordinary fall (mite be 520 cant remember) but it comes in gamers submitting how many kills it takes them to have a whip, yes its possible to have in your scope, but OSRS buy gold isnt the fall speed.