There is really no quick way - in any case it will take a long, long time.
In any case, it works faster if you are willing to spend a lot of money. I am talking about many millions here! In that case, you can buy lots of the highest-level runes that work at your level (for example, at higher levels, death runes), and attack a lot. You might also repeatedly teleport, or do high alchemy. But in any case you lose money.
If you don't have that much money, you might try one of the following; each of these alternatives is much slower:
Alching. Try to find an item that alchs for more than their value price.
charging air orbs you will accuatlly make around 400k per 1k orbs
Creating oak dungeon doors using Stealing Creation hammers
Burn maple logs once you are able to....then keep doing that to 99. This is the cheapest way to get 99 FM if you feel like spending alot of money then use higher ranked logs.
lvl 70 wc buy a ton of runes
Same as for level 99 in any other skill. About 13 millions.
Years.
I'm 99 wc and I like to chop magic trees, I make around 140k per hr.
A Magic cape can be purchased for 99,000 coins from Robe Store Owner at the Wizards' Guild by players who have achieved level 99 Magic.
99 strength and 99 magic would make a good pure. I'm not gonna lie but that would be pretty awful, unless you had 99 range too, you'd be great. Ice barrage, K0 with dark bow. ^^
Look up a magic calculator, then how many times you have to plank-make from 86-99 magic, then add the prices of the planks + runes to cast the spell together, to get the cost.
Well if you want the slowest xp but the cheapest way to 99 crafting. Well here it is, 1-99 cut opals all the way but this will take a while as in (5 months) you will need to cut atleast 1m opals but it can make you some money depending on the price of them.