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

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. Auction History:
- The average hammer price in previous auctions is 74.39 euros.
- The coin has been auctioned 26 times, of which it has sold 18 times, indicating good demand.
- Previous hammer prices for coins with similar conditions (85-90) have ranged from 45 to 190 euros, depending on the auction and demand.

3. Starting Price and Average Starting Price:
- The current starting price is 40 euros, and the average starting price in the past has been 51.41 euros. This suggests that the current starting price is reasonable, but it could be higher given the price history.

4. Recent Trends: In recent auctions, hammer prices have been higher for coins in similar conditions, especially in the 90 condition range.

Based on these factors, an estimated maximum purchase price could be in the range of 100 to 150 euros, considering that the condition is good and that the price history shows that similar coins have reached higher prices in the past.

Therefore, a reasonable maximum purchase price could be 125 euros.