In this answer, I linked to a product on Amazon to show that its price meets the question requirement. Two days later, the price dropped around 15USD. Luckily, in this case, it didn't contradict the question requirement, though now the price in the answer is different than that on the store page.
My question is about what to do on the flipside. When someone posts an answer for a product, then the next day, the price rises such that it crossed the asker's threshold. Of course that would vary from case to case, but wouldn't the site benefit from a general guideline?
How about posting answers with prices of products that are temporarily on sale at the time of posting. Should it be discouraged?
Lastly, is it possible (and is it a good idea) to embed product links in answers so that the prices are updated along with the store page?