Based on the provided data, we can observe that the coin in question had a starting price in the most recent auction of 18 euros, with an estimated price of 30 euros and a final price of 45 euros. Additionally, its condition has been described as 80 (MBC+).

Considering the previous prices of this coin, as well as its condition and the trend of final prices, we can estimate a maximum purchase price for this coin in the upcoming auction. Since the highest final price was 45 euros and the condition is 80 (MBC+), we could consider a maximum purchase price around 50-55 euros.

It is important to note that the final auction price may vary depending on factors such as demand at that specific time, competition from other bidders, and interest in the coin in question. Therefore, it is advisable to pay attention to the auction and adjust the offer accordingly.