Here's an herb calculator I used to figure out what I could get with the money I had.
http://www.tip.it/runescape/?herb
81m could take you to 99, but you'd have to do it an extremely slow way. More likely, around 92-94 if you're frugal.
I cost me around 100m to go from 70-88 Herblore a couple of months ago. I did very cheap methods like attack potions and Serums. I am sure that you could get it up fairly quick and cheap with 81m. Not to mention herbs have dropped in price substantially.
I would suggest cleaning herbs for a while, it can get you 30-50k exp per hour so it isn't too bad. You can also profit slightly off it.
Also when you get bored you can just do it the fast way, but you won't get to a high level.
You could get 99, by doing attack potions I am pretty sure. Though it depends whether you can sell them or not, and it will take a long time. Don't recommend it.
Cleaning herbs could be another cheaper method, however if anything, you could get around level 85 ish from level 1.

