Alright, these are just ideas, nothing is final:
Cost:
350 Blue = 395k
3250 Green = 1.7m
1600 Crimson = 1.3m
3100 Gold = 450k
Total Cost = Approx 4m, for 50-75.
Gold Charms:
Lev 16 Granite Crab.
Needs iron ore (buy)
Total cost: 271
Loss: 146
Green Charms:
Lev 33 Beaver.
Needs willow logs (wc own).
Total cost: 1800
Loss: 525
Crimson Charms:
Lev 45 Pyrelord.
Needs tinderbox (buy v cheaply)
Total cost: 2785
Loss: 835
Blue Charms:
Lev 55 Spirit Jelly.
Needs Jug of water (buy v cheaply)
Total cost: 3780
Loss: 1130
Level needed to exchange: (Do in this order?)
Gold: 26
Green: 41
Crimson: 52
Blue: 61