Shitty because: 50 exp in both each time, if you buy at regular price you may lose 3 or so gold. After so many times of doing this, it will add up.
1. Go down to G.E. bring all your nature and fire runes.
Buy 2 coal for every 1 Iron ore, if you don't have nature or fire runes buy those too.
Fill your inventory...
Use superheat item, turning the 2 coal and 1 Iron into a steel bar.
Sell the bars to the G.E. to make back all/most of your money.
Buying 2 coal, 1 iron, and the runes should cost a bit over 1,000; where the steel bars sell for round 1,011 or some shit, less than how much everything costs, but basically a 3 coin difference if you buy and sell at the regular price.