Based on the data provided, we can observe that the coin has had an average auction closing price of 275.08 euros in previous auctions. Additionally, the current condition of the coin is graded at 85 (VF+/EF-).

Considering that the starting price in the upcoming auction is 275 euros and the coin has had an average auction closing price of 275.08 euros in the past, we could estimate a maximum purchase price around that value. However, taking into account that the condition of the coin is relatively good (85), we could consider a slight increase in the price.

Therefore, an estimated maximum purchase price for this coin in the next auction could be around 280-290 euros. It is important to note that the final price will depend on the demand at the auction and other potential interested buyers.