Based on the data provided, we can observe that the coin in question has had an average auction closing price of 57.29 euros in previous auctions. Additionally, its current condition is graded at 75 (MBC).

Considering that the starting price for the upcoming auction is 45 euros and the historical average starting price is 38 euros, we can estimate that the closing price could fall within a similar range to the previous average closing price, around 57.29 euros.

Given that the coin's condition is graded at 75 (MBC), indicating it is in an acceptable condition but not in perfect preservation, we could slightly adjust the estimated maximum purchase price downwards.

Therefore, taking all these factors into consideration, an estimated maximum purchase price for this coin at the upcoming auction could be around 55-60 euros.