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

1. Starting Price: 20 euros. This is the initial price of the auction.
2. Condition: The coin has a condition rating of 95 (EF+), indicating that it is in very good shape. This generally increases its value compared to coins in lower condition.
3. Historical Data: The coin was previously auctioned with a starting price of 60 euros and an estimated price of 80 euros, although it did not sell at that time. This suggests that the market has a higher value expectation for this coin.
4. Average Starting Price: 40 euros. This may be an indicator of the average value that buyers are willing to pay for similar coins.

Given that the condition is high and considering the previous starting and estimated prices, a reasonable maximum purchase price could be in the range of 80 to 100 euros. This is based on the expectation that, given the condition and interest in the coin, buyers may be willing to pay a higher price.

Therefore, an estimated maximum purchase price could be 90 euros.