I'm not a proponent of prescriptive grammar; I'm also a conflicted person with a remarkable ability for compartmentalization. Thus, I will start off with a very slight correction. One does hear much about pottery 'shards,' but they don't exist. Surprise! Archaeologists do often study pottery sherds, however, as well as glass shards, if the time period is correct. This is super confusing and not especially helpful, I know, but I couldn't help myself; apologies.

Now, to try to answer your first question, How cheap or expensive was common pottery historically?

To paint with a very broad stroke, common pottery has been relatively inexpensive for the majority of its existence in human history, often made locally, even in the domestic space. For nearly that same amount of time, however, there has been uncommon pottery that would have been relatively quite expensive; pottery (or ceramics as the fancy-folk academics like to call it) has had and continues to have a wide variety of uses and disuses. For example, do you use, or even want to use, your grandmother's china set? Not so long ago, that china set might have been today's equivalent of the latest smartphone as a symbol of social status and wealth. Check out Carla Sinopoli's Approaches to Archaeological Ceramics (1991) if you want a general overview on the subject. As a personal aside, I highly respect Dr. Sinopoli as a bad ass who's made a positive mark over the last several decades in an academic environment often toxic and hostile to women such as herself.

To speak with a bit more specificity on a subject with which I am familiar (but does not answer your second question) and illustrate my point, 'high status' ceramics are routinely found within slave quarters on American plantation sites. Differentiation can sometimes even be found within different subjugated groups on the plantation, but regardless, many slaves in the American South ate off of what were once extremely 'nice pots', whether through their own purchase or through wealthier folks' hand-me-downs. For example, see Adams and Boling's now aged paper, "Status and Ceramics for Planters and Slaves on Three Georgia Coastal Plantations" (Historical Archaeology, 23(1):69-96, 1989) or George Miller's even older "Classification and economic scaling of 19th century ceramics" (Historical Archaeology 14: 1-40, 1980) for a more general overview of pottery in the horrific heyday of American plantation life.

Hopefully someone much more knowledgeable in medieval European economic history than myself will come along to answer the second part of your question.

Edited for clarity, rule compliance, and sourcing.