Based on the data provided, we can observe that the coin has had an average auction closing price of 26.91 euros in previous auctions. Additionally, the condition of this coin is rated at 90 (EBC).

Considering that the starting price of the upcoming auction is 12 euros and that the estimated closing price has ranged between 18 and 80 euros in previous auctions, we could estimate a maximum purchase price around 80 euros, taking into account the price history and the condition of the coin.

It is important to note that the final closing price may vary depending on the demand at the auction and other factors that may influence buyers' decisions.