It's clear how much the Everbright Flame costs. Even if we set aside the fees for hiring spellcasters, this thing requires at least fifty Gold Coins because it needs the ruby powder worth fifty Gold Coins evenly scattered over the casting spot to ignite this Magic Flame.
If it were just one or two Everbright Flames, even ordinary merchants could afford to use them.
But don't forget, this is a tunnel more than eleven kilometers long, with an Everbright Flame placed every ten meters, crisscrossing along the walls on both sides, meaning there's one every five meters. Just for this feature alone, the tunnel would require an investment of over two million (covering the cost of materials and the wages of the spellcasters, even for War Mages trained by the Komeer Kingdom, who would still require payment, albeit at internal prices, which are relatively cheaper).
