Pretty simple math really. The C4 charge cost less than 3g each, and every chest has at least 5-6g in straight coin. Plus potions, greens/blues, etc.

On my server, primal fire = 25g, primal earth = 5g, and fel iron bar = 1g. So the cost break down is:

1 mote of fire 2.5g
2 mote of earth 1g
8 fel iron bar 8g

This makes 2 batches, or 4 elemental seaforium charge, so cost is 2g 87s 5c each.