Based on the data provided, we can observe that the coin in question had a starting price of 30 euros in this auction, with a conservation grade of 30 (BC+). Additionally, it has been auctioned in the past on four occasions, being sold each time.

The previous prices of this coin have varied, with starting prices ranging between 15 and 90 euros, and estimated prices between 25 and 150 euros. The final auction price has been higher than the starting price in most cases, with an average of 85 euros.

Given that the average starting price in this auction is 52.5 euros and the average final auction price has been 85 euros in previous auctions, and considering the conservation grade of the coin is 30 (BC+), we could estimate a maximum purchase price around 90-100 euros. This takes into account that the final auction price in previous auctions has been higher than the starting price in most cases.