Based on the data provided, we can observe that the coin in question has had an average auction closing price of 516.78 euros in previous auctions. Additionally, its preservation has remained at a high level, around 95 (UNC-).

Considering that the starting price for the next auction is 300 euros and the historical average closing price is 516.78 euros, we could estimate a maximum purchase price around that value. However, taking into account that the historical average starting price is 437.5 euros, we could consider an estimated price range between 437.5 and 516.78 euros.

Given that the coin's preservation is high and it has performed well in previous auctions, an estimated maximum purchase price could be around 500 euros. This price falls within the historical price range and considers the quality and demand of the coin in question.