Do you want prayer or straight atk/str/def levels? Which ought to decide for you. I personally would prefer with more prayer so I would head to RS gold mountain giants. Following the 40s I would say hill giants for extra prayer and flesh crawlers as previously mentioned. Things will not change much until the fifties when moss giants can be an alternate to hill giants. Once you reach the sixties you can then also consider stronghold of security spiders.
Alright, so I want most of the fundamentals, I'll post what equipment I think and if you could edit it for me it'd be good, and tell me the approach, I have a vague notion but experience would help. I have 87 Magic, 80 Defense and 83 Hitpoints, if those stats aren't sufficient I would likely instruct them so let me know. Also, I am aware soloing rex might involve killing prime and supreme, so for reference my range level is 79 (80 easily), and 82 Strike and Power. I am mainly doing this for money, therefore if rex really isn't good cash anymore/ever that would be nice to understand as well. Thanks.
Should you apply the Burstinglobs buddies chat, there is always someone who is hybridding and needs a solo mage partner to kill Rex for them whilst they kill Supreme and Prime. This means that you don't need to fret about Supreme or Prime whilst you're down there, unless both of you are bad at what you are doing. I would take Tubby's set up with mystic boots and a Ring of Life until you are confident, then you can begin risking a bit more expensive gear.
When there is absolutely no one in Burstinglobs searching for a solo mage, simply ask if anybody is hybridding/tribridding and will allow you to hop worlds from theirs, simpler than needing to kill Supreme/Prime to start your journey. Bring a tortoise and make sure you have a brew:restore ratio of 3:1. If you can, bring 2 fruit bat pouches and scrolls for if your tortoise expires, fruit fall is simply good for soloing Rex, then it is buy rs gold paypal not really efficient in case you are hybridding/tribridding.