Based on the provided data, we can observe that the starting price of the coin in the upcoming auction is 250 euros and its condition is 85 (ebc-). Additionally, previous auctions have resulted in closing prices ranging between 230 and 440 euros.

Considering that the coin has been auctioned 175 times in the past and the average closing price has been 298.77 euros, we can estimate a maximum purchase price around 350-400 euros, taking into account the condition and previous closing prices.

Therefore, an estimated maximum purchase price for this coin in the upcoming auction could be around 350-400 euros.