If the identifier is an SKU, it seems to follow that to distinguish between different prices one could have an additional "version" identifier? Or perhaps even

If the identifier is an SKU, it seems to follow that to distinguish between different prices one could have an additional "version" identifier? Or perhaps even a more generic on-this-date parameter, in this case representing date of quotation (which then dovetails quite nicely with the expiry mechanisms already built into HTTP).