It is possible to alch and actually make profit.
The way is simple, but takes time.
the materials you need are:
Yew logs (480 ea)
Flax (55 ea)
Nature Rune (230 ea)
This leaves you with a total of 765. Use the Flax to spin Bow Strings, and a knife and Yew Logs to cut Yew Longbow (u). Now make Yew Longbows. Then start alching them. Yew Longbows alchs for 768 each, which gives you a profit of 3 gp per alch (obviously depending on the price you buy for).
from 55 - 99 Magic, you need to alch 197967 times. 3 x 197967 = 593901 GP all profit from 99 Magic.
In addition, you wil get level 84 crafting for spinning 197967 bow strings and a total of 29.7m fletching XP from completing 197967 Yew Longbows.
I really hope this wuick guide was for any help to you on your way to 99 Magic. And remember that this is a time consuming way to 99 Magic. you can easily buy some of the Yew Longbows just to shorten the time, but that is completely up to you.