1 big gold coin =>50 gold coins

1 gold coin => 20 silver coins

1 silver coin => 10 big copper coins => 100 little copper coins

When gold isn't enough, precious gems or rare materials can be used to exchange.

-- EQUIPMENT --

Most of the existing equipment is pretty basic, armour made of leather (simple, studded, reinforced with bits of metal...) and weapons forged with iron or steel alloy.

Anything better needs to go through the hands of master craftsmen capable of magic, usually followers of Nyx, Theomars or Monte. These experts are capable of creating new alloys, engraving magic circuits and infusing materials with their power to give their creations unique capacities.

Broke elementalists can exhaust themselves in order to create elemental crystals and sell them, which are then used in alchemy and crafting.

tl:dr

BASIC : leather / iron / steel works.

ADVANCED : uncommon alloys and simple runes. Require magic use during the making.

EXPERT : composite runes and elemental works through crystals. Requires a huge quantity of magic and special resources.

MASTER : custom works requiring the client's own magic to be imbued in the product. Crafting effort can vary enormously depending on what is desired.

RELICS : items owned by the Gods of Men before their ascension, which followed through their deification. They are usually wielded by the Children of the Gods, if they remember where they left them, and hold incredible power. Time, Nature and Element don't have relics, but can nonetheless create some on a whim or to reward followers and god-candidates. The Gods of Men can make some too, but it is much rarer as they already have their own stuff. Relics are particular in that they contain traces of divinity, and can thus choose and refuse a wielder.

-- Potions and magical reagents --

Nothing much to say here. Potions are common goods with simple effects such as healing, coloring or feeding. They are NOT MAGIC in any way, and won't grant anything fancy like flight or invisibility (see relics for that). The only exception would be alchemical lights, which works pretty much like a mix of dynamo and glowsticks. Shake it and it'll glow.

Magical reagents are a pretty vast theme and usually encompasses anything magic. Charged gems, elemental crystals and aligned materials, resources from Blessed and mythical creatures... and what they are used to make.

Golems are halfway elemental magic and magical reagent, since they need the first to make them and give them intent, also the second (a charged gem) to provide it energy.

--GENERAL TL;DR --

Oh come on. You fell for that? This is a book, what are you doing if you don't read?