Well, as the title says.

 

Also, I'm currently 72 Herblore, and I've got around 200M available for the project.

 

Thanks in advance.

Well the best way to do it once you reach 82 is to the best next available potion, cause you don't wanna be stuck with 20k of a said untradable just cause it was cheapest to make. In terms of getting to 82, it really doesn't matter, all of them are pretty close to the same gp per xp imo.

http://runescape.wikia.com/wiki/Calculators/Potions

 

Like everything including extreme potions (lantadyme rose to 6k each, extreme defs used to be good) is 25+ gp/xp at the moment. That pretty much means you're looking at at least 300m to get 99 herblore, plus most stuff is either unbuyable or crashing. The market is really unstable, the only relatively safe thing to do would be training with serum 207, which is like 90k xp/hour if you buy unf pots and still pretty expensive.

I'd advise against getting 99 at the moment, maybe get 90 to unlock the useful pots and get 99 when the market is stable again (will probably take a while).

Wow 300m? Might as well forget about that :D

 

Maybe I'll try prayer..

I got herblore exp at under 20 gp/exp, by making super energy's with mort myre fungus and a clean avantoe, and then using a papaya to make those restore special potions. You get 317.5 exp in total, for a cost of around 5.5k for a mort myre fungus, avantoe, and a papaya. But when I bought them, avantoes were still 1.6k, and papayas were at their peak at 2.8kish. Now avantoes are higher, and papayas are crashing, so it should still be under 20 gp/exp. I'm not exactly sure on current prices, so look those up if you're interested.

I bought most of my super energies at around 1.2k each and I'm planning to buy papaya's at around 1.8k each so that's only 15gp/xp. Just wait out the good moments to buy ingredients.