400 energy = 500 radiant fire crystals
200 energy = 500 shinning fire crystals
100 energy = 500 glowing fire crystals
50 energy = 500 2* fire crystals

Then, make it to where 3* and 4* fire crystals are quite a bit more rare- think 1/5 as common as they are now for 3* fire crystals and 1/10th as common for 4*. Make 5* orbs harder to get (since those are silly) and you've got the whole mess sorted-

Crafting Thing...Source...Subsource
Materials...Monsters...Grim/Forge/Primal Sparks
Orbs...Boxes...Supply Depot
Fire Crystals...Supply Depot...Boxes

Where the source is the main flow and the subsource serves the purpose of equalizing drop rates- if you have A TON of energy, you can spend some of it on orbs in addition to fire crystals. If you have a ton of time you can spend it on getting fire crystals... but generally, you'll be buying fire crystals and finding orbs/materials.

You might be thinking that this would lose profits because they cost a lot less. Many players tend to pay the following when crafting gear:
600 energy = bought 2*, too lazy to farm T2 orbs, generally T3
250 energy = 2* + 3*, found 4* orbs, generally early T3
0 = farmed the whole thing, the 'true F2P'/"smart player" that enjoys T2/T2 player

With this, those same players would be more likely to spend:
1,300 = bought additional fire crystals, merchants and players that know what's up
650 = 5* fire crystals + 250 on orbs, farmed the big stuff
500 = farmed as much as possible, bought 5* and 3* fire crystals
400 = farmed everything, bought 5* fire crystals