Based on the provided data, we can see that the coin has a conservation grade of 30 (BC+), indicating that it is in an acceptable but not excellent condition. Additionally, it has been auctioned once in the past and sold for an average price of 70 euros.

Considering the coin is in an acceptable condition and taking into account the previous average auction price, as well as the fact that it will be auctioned only once on this occasion, we could estimate a maximum purchase price around 75-80 euros. This is considering that the starting price is 18 euros and the previous average auction price was 70 euros, so it is likely that the auction price this time will be higher.