Based on the provided data, we can see that the coin in question has a starting price of 18 euros in the upcoming auction. It has been auctioned a total of 5 times in the past, being sold 4 times and not sold once.

The average starting price in previous auctions has been 25.6 euros, while the average final price has been 45.5 euros. The condition of this coin is described as "30 (BC+)".

Regarding the previous prices of this coin, in the last auction recorded in September 2022, the starting price was 30 euros and the estimated price was 45 euros. However, the final price is not available in this case.

Given that the condition of the coin is at an acceptable level (30 - BC+), and considering the previous auction prices where the estimated price has ranged between 40 and 50 euros, we could estimate a maximum purchase price of around 50 euros for this coin in the upcoming auction. It is important to note that this is just an estimate and the final price may vary depending on demand and other factors at the auction.