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

1. Coin 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 Auction Prices: By looking at the hammer prices of coins with similar conditions (around 80-90), we can see that the hammer prices have varied. For example, in recent auctions, coins with a condition of 80 have reached hammer prices between 54 and 95 euros.

3. Starting Price and Average Hammer Price: The current starting price is 90 euros, and the average hammer price for similar coins is 69.5 euros. However, since the condition of this coin is superior, we can expect the hammer price to be higher.

4. Auction Trends: The coin has been auctioned 110 times in the past, with a high sales percentage (104 out of 110). This suggests that there is consistent interest in this coin, which may increase its value.

5. Recent Hammer Prices: In recent auctions, we have seen hammer prices reaching up to 320 euros for coins of similar condition, although this may be an exceptional case.

Based on these factors, an estimated maximum purchase price for this coin could be between 120 and 150 euros. This is based on the condition, interest in the coin, and the hammer prices of similar coins in the past.