Actually, a money-based infrastructure was important to Celts (just being pedantic, it's the EB way). I don't know about Germans and the like, but Celtic leaders had little power outside of the military; mounting tiers of 'senate'-like organizations of citizens of a kingdom voted on pretty much everything, and laborers were generally paid (Celtic coinage was so widespread because of their necessity to pay soldiers and workers); people couldn't just be ordered around by a despot, due to a series of early checks and balances; this format, mixed with Greek governmental forms, led to what we recognize today as the democratic republic (you could argue it's based on Saxon law from Britain, but that was merely aping Celtic law anyway, due to the huge number of culturally Celtic people under their rule at the time, mixed with a kind of despotism that Saxons practiced before conquering Britain). They differ from Romans and such in that they had no 'payscale'; everyone was paid based on the quality of their work, so no such thing as a salary existed. Better warriors and soldiers (and there was a difference; technically the 'warrior' was a part-time soldier, much like modern 'reservists', and soldiers did nothing but serve in the military) were paid more; likewise, a better construction laborer would recieve compensation for superior work. It's notable also, in Celtic law, that if something broke, one could sue (the modern terminology) the crafter; the argument would be based on if the owner had been negligent or otherwise led to the destruction of the purchased object, or if the crafter had simply been careless and the object broke due to creator failure. Anyway, as it boils down, paid labor for Celts is extremely important. Even slaves were paid (though common courtesy demanded far less; they were usually paid by good graces of their masters, who would recieve the payment, and reward his slaves based on the quality of work; many Celtic laws from various regions point that a slave must be paid SOMETHING, assuming he's done any work, but that doesn't mean it necessarily has to be that much).

Everyone assumes Celts were warriors purely (and this brings to mind despotism; a kind of 'rule by strength' concept, which is misconcieved). This misconception comes about because the most extensive accounts in writing come from the Romans, who did little but fight with them, but it ignores the huge trade economy they generated, and a great number of important, but easily overlooked, notations. Celtic kings attracted additional soldiers by promising slight pay 'bonuses', greater than opposing kings. They funded these by trade networks; Bibrax, Gergovia, Camologos, Camolodunum, Menapia, and numerous other cities were major trade centers and generated trade income comparable to mediteranean traders. Even the name 'Briton' comes from nothing that they were tin traders (and extremely wealthy because of it). The favored coinage metal of Celts was silver, more valued than gold (gold was valued, but more as ornamentation; too rare to form a solid coinage system around it). It can be argued best, based on both written and archaeological sources, that, while they were a 'warrior' culture, Celts were at the same time a merchant people. They traded with everyone, including their enemies; the Romans were at one time considered jealous of the wealth of Gaul, and one joke said an ambitious Gallic king was considering buying the city of Rome, but felt it was too small for his ambitions. Celts were coinists and adored rare metal; Brennos demanded his weight in gold to leave Rome. Huge coin hordes are found all over Gaul, Britain, and Ireland; presumably hidden treasure troves to be used as fallbacks, or as a kind of 'retirement fund'; Celtic kings rarely served out their whole life as king. When one was incapable of commiting to open combat, they were then on ineligible to be king (since the 'king' is not a monarch as in the feudal era, but an elected military and vaguely administrative leader). So, an elderly or crippled former king might want something he and his family could fall back on. Clearly, coins were important; money was important. Everyone needed it, and all of society was based on the silver coin in some way; Celts traded other things though too. Weapons and armor were very valuable, as were horses, chariots (for war, but also travel, and just for show), livestock, crops, pets of all kinds, especially exotic ones (an ancient Celtic king in Ireland had a baboon, likely from a Carthaginian trade partner as a coronation gift), etc. In Ireland and Wales, since the law existed long enough to be commited to paper (so we don't rely on second and third hand accounts of non-Celts), we get a better look at what exactly Celts thought of trade and payment. Kings and other 'nobles' (since Celtic nobility is more of a business based aristocracy), to be elected, were expected, often, to own their own business, be able to afford to pay most of the soldiers through it (Celts taxed, but they weren't fond of it and tried to keep taxes low), be able to afford feasts and events, always be ready and able to pay back debts, or fines if they were sued, etc.; these requirements again point to the importance of money, and, because of that, trade. So, the Celts were clearly a trade and business based economy (and culture, in a large sense, during the period depicted in EB and later). As for other barbarian cultures, the Iberians I do believe were, but of Germans and the like, I have no idea.