Based on the provided data, we can see that the current starting price of the coin in the auction is 30 euros and it is in a conservation grade of 30 (BC+).

Furthermore, in previous auctions, it has been sold for closing prices of 80 and 85 euros, with estimated prices of 80 and 100 euros respectively. The conservation grade in the last successful auction was 70 (FDC).

Considering these data points, we can observe that the coin has experienced an increase in its closing price over time. Given that the current conservation grade is lower than that of the last successful auction, we could expect a closing price in the range of 80 to 85 euros.

Therefore, my estimate for the maximum bidding price for this coin in the current auction would be around 85 euros. It is important to note that this is just an estimate and the final price may vary depending on demand and other factors in the auction.