Right now alching supplies(longbows etc) are extremely expensive. If you want to get 94 mage for about 1/4 of the price, super heating iron ore is a great option.
Iron ore goes for 60-75 gp each and iron bars go for 200ea. So you only like between 80-95gp/alch as apposed to losing up to 220 depending on nature rune prices.
So far I am 91/94 mage, also 67 smithing.
You get 265 mage xp and 62.5 smithing xp per cast.
So a side benefit is that you can get 70+ smithing while you do it.
If you want any additional info let me know