The current price is the lowest in-stock price we have for that model right now. If no shop has it in stock, we do not invent a price to fill the page.
The 90-day low is the lowest price we recorded in the last 90 days. The median is the middle of those recorded prices, so one unusually low day does not set the usual price by itself.
A good price is at or under that 90-day low. Around the usual price means the current price is above the low and at or under the median. Above the usual price means it is over the median. We make that call only after at least three prices have been recorded in the window. Fewer than that, and the badge says we do not have enough history yet.
Shipping, a transfer fee, and a mail-in rebate are not part of the number unless the shop printed a shipping cost on that listing. The price at the shop's checkout is the one that counts.