Based on the data provided, we can observe that the coin in question has had an average auction closing price of 91.81 euros in previous auctions. Additionally, its condition has been described as '70 (MBC-)'.

Considering that the coin's condition is good but not excellent, and that the average closing price has been 91.81 euros, we could estimate a maximum purchase price around 100-110 euros. Given that the starting price in this auction is 25 euros, it is likely that the final closing price will be higher than the starting price, but it is difficult to predict exactly how much.

In summary, an estimated maximum purchase price for this coin in the upcoming auction could be around 100-110 euros, based on historical data and its condition.