Ok alching is expensive as shit, you basically lose the whole value of the nat no matter what you alch. Stun alching is even more expensive.
What i did was superheat iron ore alllll the way to 94. Iron ore buy for 80-90 gp ea, bars sell for 250. So, you are getting around half the value of the nat back, sometimes less, sometimes more. Now that's all good but you also get smith xp for every bar. Doing 50-94 mage got me 79 smithing.
There are lots of alternatives to alching, consider this one=)