I believe Heat Amp prices are ridiculous. They're timed items, just like trinket slots and weapon slots, but the only thing they do is double the amount of heat you get per level completed. Not 10x, not 5x, nothing to justify their prices (1 week heat amp costs what, same as 2x trinket + 2x weapon for a month?)
I offer to simply these items:
30 days (because I'm greedy) heat amp, doubles heat. Costs 300 energy. Could be 7 days for 300 energy, but not 2 days for 300 energy, I don't play much.
With this price I'll buy it every time I'm heating something. How often are they bought right now? I doubt they're bought at all, even though they're extremely useful.
They could also provide another useful feature: increase rate at which heat crystals drop (every crystal picked up becomes 2 crystals, for example) since I'm really short on Radiants now... Upgraded 1-2 items and my 1000+crystals are gone.
They carry the same price tag as when they were the most useful for players to progress toward for their gears before the removal of elevator costs, in that sense that's the justification for their price. Though now I'll agree that it doesn't hold up just as well anymore. Heat Amplifiers have no particular uses outside of genuinely heating your gears faster (you will require getting past the Forge paywall at a faster frequency to do it justice) as well as building up appetite for your Battle Sprites faster (unequip unheated gears for best effects).
I am still waiting on level-up via regular heating to return, so I don't think much of reducing their cost for what they are now: if they were, the moment the Forge isn't mandatory for leveling up anymore they would be way too accessible for such a staggeringly low price and OOO wouldn't remotely be able to profit from it without breaking the game's flow. Even in hindsight, a mere 300 Energy for 30 days of double heating results is incredibly selfish.
As for Radiant Fire Crystals, I don't see a reason not to slightly lower the Forge paywall.