1-99 = 500,000 curses.
Providing the autocurser on the bot does 1k curses per hour it'd take you 500hours. So if you bot it for 5hrs a day it'd take you 100 days, so just over 3 months.
Not going to say its the quickest way but its most cost effective way as 500,000 at 20gp ea would cost you 10mil whereas alching, planking, humidifying would cost considerably more.
Bot the curses for about 10-15hrs a day and it'd only take you about 1month to get 1-99 magic.
I know 1-82 for ice blitz would take about 70,000 curses, thats if you are going for ancient magiks.