All prices not listed are relatively fine in my books.
Fire Crystals
Warm Fire Crystal x50... 10 E
Glowing Fire Crystal x50... 50 E
Shining Fire Crystal x50... 100 E
Radiant Fire Crystal x50... 200 E
Fire crystals were never a part of the original Spiral Knights, and have increased the price of gear by 10x. Players, unfortunately, do not value gear by 10x more than they used to.
Old price of gear in energy, from 2* to 5* = 800+400+200+50 = 1650 CE
New price of gear in energy, 5* level 1 to 5* level 10 = 6,300 E
What I'm proposing as the price of these fire crystals to heat 5* gear: 1,800 E
The tax is still there. Every 5* weapon still requires heat... the difference is that with cheaper prices, more players will consider paying the tax, and more tax in total is likely to be paid, and more weapons get crafted and used. It's a win win situation.
Keys
Shadow Key x4... 1,800
Shadow lairs aren't what they used to be, and could be used to farm in. The only issue is how pricey it is to visit said shadow lairs. If these prices were lowered substantially, I'd be much more inclined to buy shadow keys on the double. Perhaps, as compensation, only the primary key user could receive the shadow lair material. That would make shadow lair materials cost the same as they always have.. in terms of energy needed to forge them.
I do believe fire crystal prices should be lowered. However I personally feel like if we wanted to make it balanced, we should use elevator depth prices. Divide the total cost of crystals by 10 and you'll get how many depths we are currently "expected" to completed (under the old system). Pretty easy to see the 5* one being obnoxiously overprice. 70 levels of grinding for 1/9th of a level 10 weapon is not accurate or balanced whatsoever.
Would be better if radiants were closer to, say, 30 levels. 30 * 10. So 300 energy per 50. That's 2700 energy for one 5* item's heat, making buying orbs + all the radiants needed be equal in price to the supply depot 5* item. It's cheaper than buying it however, since you'd have to buy crystals and the item, but it makes for a familiar number.
Next up, I don't think crafting prices need to change. The 4* grind already is severely offputting to players, making them more reliant on grinding will not encourage anyone to stick around longer.
Shadow Keys really ought to be something we can buy with guild money as well as from the depot for energy. Give officers and higher the ability to purchase shadow keys in the guildhall which is then placed in officer storage, and any officer can take them from there. I'd say give them a price like 200k crowns so that it's more expensive than buying it from the depot, but it's the work of a guild for something rather than individual effort (also gives a reason for guilds to stockpile crowns and acts as an additional crown sink. Guild bonds can also be played with more).
Making shadow keys cheaper is sorta eh. I like the idea of more shadow lairs, but the artificial keeping them rare prevents endless grinding. Sure, more end-game grinding areas would be wonderful, I just don't think shadow lairs should become an easy normal instead of being a difficult end-game challenge that players new and old can look at with anticipation.