Based on the data provided, we can see that the coin in question has had an average auction closing price of 46.48 euros in previous auctions. Additionally, its current condition is graded at 95 (EBC+).

Considering that the starting price in the upcoming auction is 30 euros and that the coin has been sold in the past for prices ranging between 12 and 100 euros, we could estimate a maximum purchase price of around 100 euros, taking into account the condition and previous closing prices.

Therefore, my estimation of the maximum purchase price for this coin in the next auction would be around 100 euros.