Based on the data provided, we can observe that the coin in question has had an average auction closing price of 67.06 euros in previous auctions. Additionally, its current condition is 90 (EBC).

Considering that the coin will be auctioned in the upcoming days with a starting price of 30 euros, we can estimate a maximum purchase price based on the average auction closing price and the current condition. Given the high condition (90), it is likely that the closing price will either remain stable or slightly increase.

Therefore, my estimation for the maximum purchase price of this coin in the next auction would be around 70-75 euros. It is important to note that this is just an estimate and the final price may vary depending on demand and other factors in the auction.