Based on the data provided, we can observe that the coin has had an average auction closing price of 84.29 euros in previous auctions. Additionally, the condition of this coin is rated at 25 (BC).

Considering that the starting price for the upcoming auction is 30 euros and the historical average starting price is 60.14 euros, we can estimate that the closing price could be around 90-100 euros.

Given that the coin has previously sold for up to 110 euros and considering the upward trend in closing prices, we could estimate a maximum purchase price of around 110-120 euros, taking into account the condition of the coin.

Therefore, my estimate for the maximum purchase price for this coin in the upcoming auction would be around 110-120 euros.