Based on the data provided, we can observe that the coin in question has had an average auction closing price of 75.46 euros in previous auctions. Additionally, the condition of the coin has been described as '70 (MBC-)'.

Considering that the condition of the coin is good but not excellent, and that the average closing price has been 75.46 euros, we could estimate a maximum purchase price around 80-85 euros. Given that the starting price in this auction is 25 euros, it is likely that the closing price will be above this value, but it should not significantly exceed the historical average closing price.

Therefore, my estimate for the maximum purchase price for this coin in the upcoming auction would be around 80-85 euros.