Well I made 10m in 6 days fishing sharks, but now sharks are dropping, so I'd say a maybe 2-3 months if I botted for more than 8hrs a day. I usually only bot for about 4-5 hours max every couple of days.
Depends on your stats really.. If you are maxed (or near to maxed 110+cb) then you can join gwd teams and do cs, ls or even ffa. You can easily make more then 100m in a month. If you're lucky you can make it in 2 weeks with gwd maybe more.
When I used to play I would Graak nature running I could no life and do 100k nature runes in a day and a bit. so you work it out, I don't know prices of nature runes anymore :S