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

1. Starting Price: 60 euros.
2. Condition: The coin is in a condition of 80 (VF+), indicating that it is in good shape.
3. Auction History: It has been auctioned 2 times in the past, of which it sold once and did not sell once. This suggests that there is interest in the coin, but also that there may be some resistance to paying more on certain occasions.
4. Average Hammer Price: 75 euros, which is the average price it has sold for in the past.
5. Previous Estimated Price: In the 2017 auction, the estimated price was 90 euros, and it hammered at 75 euros.

Given that the condition is good and the average hammer price is 75 euros, but there is also a previous estimated price of 90 euros, we could consider that the maximum purchase price could be in a range between these two values.

Taking into account the information and the interest in the coin, an estimated maximum purchase price could be approximately 85 euros. This falls between the average hammer price and the previous estimated price, reflecting a reasonable value for a buyer looking to secure the coin in good condition.