From the Oxford University Press blog:
Strange as it may seem, the origin of the verb buy remains a matter of uninspiring debate, at least partly because we don’t know what this verb meant before it acquired the modern sense. To us the process of buying or purchasing contains no mystery: it refers to obtaining goods in exchange for money. However, in the remote past, people did not buy goods: they produced them for their own consumption or exchanged them for other goods. Characteristically, money and mint are words of Romance origin. Purchase is also a borrowing from Old French, and it, too, meant “to obtain, to acquire,” rather than “to buy.” In our oldest Germanic texts, gifts were often exchanged but hardly ever sold and bought. Though the corpus of Old English texts is not so small, the verb bycgan, the ancestor of buy, occurred in the extant literature only in the twelfth century (that is, with regard to Old English, very late). At that time, it meant “to redeem, to ransom.” A century later, this verb turned up with the sense “to expiate.” The sense known today is later.
In the Germanic-speaking world, only Icelandic preserved rich old native prose, and, while reading the sagas, one notices with surprise how seldom any goods are bought or sold. Money existed and was greatly valued, but no one ever “went shopping.” Silver and gold, and artifacts made of precious metals, were constantly used as gifts and as compensation for murder and other crimes, but banks, money lenders, usurers, and the many appurtenances of later economy did not exist. Yet one could buy a ship and a slave. One of the central characters in The Saga of Njal tried, at the time of famine, to buy hay and cheese from a neighbor, but this is not a typical case. Anyway, the neighbor turned down the request, and we don’t know the details of a possible bargain. In another story, the king wanted to buy a polar bear. Thus, trade was not the backbone of their economy. Curiously, a cognate of bycgan existed in Old Icelandic, but this verb, spelled byggan, meant “to buy a wife; marry” (exactly as in Hebrew: makar!) and “to lend or lease.”....
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