To estimate a maximum purchase price for the coin in question, let’s consider the following factors:

1. Starting price: 60,000 euros.
2. Average hammer price in the past: 80,000 euros.
3. Condition of the coin: 100 (S/C), indicating it is in excellent condition.
4. Auction history: It has been auctioned once before, with an estimated price of 50,000 euros and a hammer price of 80,000 euros.

Given that the coin has a high condition rating and has reached a hammer price of 80,000 euros in the past, it is reasonable to consider that interest in this coin could remain steady or even increase, especially if demand is high.

Taking into account the starting price of 60,000 euros and the previous average hammer price of 80,000 euros, an estimated maximum purchase price could be in a range between 80,000 and 90,000 euros, depending on the competition in the auction and the interest from collectors.

Therefore, an estimated maximum purchase price could be 85,000 euros.