To estimate a maximum purchase price for the coin in question, we can consider several factors based on the provided data:

1. Current Condition: The coin has a condition rating of 90 (EF), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Previous Prices: By looking at previous auction prices for coins with similar conditions, we can see that:
- In 2019, a coin with a condition of 95 sold for 160 euros.
- In 2018, a coin with a condition of 80 sold for 120 euros.
- In 2019, a coin with a condition of 85 sold for 76 euros.

3. Average Auction Price: The average auction price for this coin is 82.19 euros, which is also a good indicator of the expected value.

4. Starting Price: The starting price is 75 euros, suggesting that the seller expects a reasonable price, but it may not reflect the true market value of the coin.

5. Auction Trends: The coin has been auctioned 18 times, of which 17 have sold. This indicates good demand and consistent interest in the coin.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 100 to 130 euros, considering that the condition is good and that previous auction prices for coins of similar condition have been higher.

Therefore, a reasonable maximum purchase price could be 120 euros.