Based on the provided data, we can observe that the coin in question has had starting and estimated prices ranging between 10 and 30 euros, with final prices reaching up to 40 euros in the past. The current conservation grade of the coin is estimated at 30 (BC+), indicating that it is not in the best condition, but also not in the worst.

Considering that the average final price has been 19 euros and the current starting price is 12 euros, we could estimate a maximum purchase price around 25-30 euros, taking into account that the coin will be auctioned in the upcoming days and has achieved higher final prices in the past.

It is important to note that the value of a coin in an auction can vary depending on factors such as demand at that specific moment, competition from other bidders, and the perceived conservation grade of the coin. Therefore, it is advisable to pay attention to the auction and adjust the offer accordingly.