To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Starting Price: 75 euros. This is the initial price of the auction.
2. Auction History: The coin has been auctioned once in the past and sold for 80 euros, which is the average hammer price.
3. Condition: The coin has a condition rating of 30 (BC+), indicating that it is not in the best condition, but it is also not among the worst.
4. Average Starting and Hammer Prices: The average starting price of 62.5 euros and the average hammer price of 80 euros suggest that interest in this coin may be moderate.

Given that the coin has a starting price of 75 euros and considering that it was sold for 80 euros in the past, an estimated maximum purchase price could be slightly above the previous hammer price, but it must also take into account the current condition.

Taking all these factors into account, an estimated maximum purchase price could be approximately 85 euros. This allows for a small margin above the previous hammer price, considering the possibility that interest in the coin remains steady or increases slightly in this auction.