As far as Herblore and herbs here is touched, good example(nowadays):
Requires 74 Herblore, or ~1M exp.
Grimy/Clean Snapdragon - 9 - 10K each at best.
Red Spider Eggs - 10K each at best, better yet(As I would suggest), grab super anti-poison(costs 10 - 15K) which grants immunity to poison for 40 minutes. You can make tons of eggs during that time at Poison Spiders.
Vial of Water(if you're too lazy to make it yourself) - 1k each(max 2k each as I saw recently).
Super restore(3) - 25 - 30K each(and it sure sells quickly)
You do the math. And it's only one potion. What if you make 100? 1000?
You can make profit all the time with these, no matter you buy or/and especially, if you gather supplies themselves.
There is more potions but this one is superior to others I think.
Here's decent profit example for Y'all.
Till then - Prayer Potions are your best friends.
I'm yet to know a person who doesn't need prayer restoration potions at all while Pking/PvMing.
Just for record, tested this week.