Personally, I'd urge the Karamja dungeon, only outside of this Tz-Haar Region. There is a whole host of options for this particular one; You can melee them in there, using a regular weapon, food and a bunyip if you can. Or you could halberd them by a safe place, or use array from a secure spot, which makes it meals free. Or there is the option of a cannon you could try either on it's own, or using the mixture of RS gold any of the above mentioned. Obviously, there are different locations, though I'd advise this area for sure.

Just realised that the title says greaters, but the article says lessers. If the endeavor is really greaters, then my only recommendation would be the dungeon in brimhaven. It is possible to use any of the aforementioned options, though you have to contend with all the terror dogs also. Sadly, there aren't a range of great options for greaters (no pun intended), however, you just have to soldier on whether it is these.

Inventory: Range equipment for Ahrim (including rune xbow). Legislation and Blood Runes for Kharyll teleport (unless utilizing home teleport with Kharyll portal). Spade. Monkfish.

Strategy: Visit Karil first. Pray attack hindsight, power prayers, and protect from range, and strike him with your special attacks. Finish him off with your ice spell. Run out. Proceed to Ahrim. You need to still have nearly 30 prayer points. Switch to range equipment, plead magic (and eagle eye if you have it). Run out if he's dead. Go to Dharok next. At this point, you should have around 1-5 prayer points left. Pray melee because of his first hit, hit him once with ice blitz, and measure away. You can usually get in 5 hits; he will start moving on the fifth hit, so you should be far from him if you would like to become in 5, otherwise only hit him 4 times and hide behind his tomb. After a couple moments, run into some far corner from him and struck him before he reaches you, and replicate. Finish him in such a manner.

Take on the remaining 3 brothers in the exact same fashion you did Dharok in almost any order you choose. Things to do for the tunnels: Depending on which brother you get in the tunnels, place your quick prayers into the correct protection. When he appears, do not panic (you are going to endure the first couple hits), prayer pot quickly, and reach fast prayers. Finish him. The thing which will consume the majority of cheap OSRS gold your food is your tunnels, so know the design and reach the chest as quickly as possible. When you reach the puzzle, if you are not exceptionally quickly, take one step back from it, then hit the monster attacking you using an ice spell, and you have 10/15 seconds to do it.