Based on the provided data, we can observe that the coin in question has had an average auction closing price of 299.94 euros in previous auctions. Additionally, its current condition is 95 (EBC+).

Considering that the starting price in the upcoming auction will be 400 euros and the estimated average closing price has been 299.94 euros, we can infer that the closing price could be in a range close to that value. However, given that the coin's condition is high (95), it is likely that its closing price will be on the higher end of that range.

Since the maximum estimated purchase price has been seen in previous auctions at values like 450 euros, 500 euros, and even 470 euros, and considering the upward trend in closing prices, we could estimate a maximum purchase price around 500 euros for this coin in the next auction.