Depends from what level. Doing Pryamid Plunder would be extreamly quicker however. 99 theiving PP would take around 2 months depending on how long you play, and master farmers I would say 3-4 again, depending on how long you play.
theres a few ways i would do-
coshing bot about 100k an hr...the fastest- no money
sorc garden fruits- idk the exp but easily bottable -no money
i would not do master farmers at low lvls its liek 15k an hr at 55 thief- about 60m ...seen alot of gp pure 99 thief/60m so im guessing its basicly 60m