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 value compared to coins with lower conditions.

2. Auction History: By looking at previous hammer prices for coins with similar conditions, we can see a price trend that may help us estimate the current value. For example, in past auctions, coins with conditions of 85 and 90 have reached hammer prices that varied significantly, but often exceed 200 euros.

3. Starting Price and Average Hammer Price: The current starting price is 150 euros, and the average hammer price in the past has been 105.85 euros. However, since the condition of this coin is above the average of auctioned coins, it is reasonable to expect that the hammer price will be higher.

4. Recent Trends: In the most recent auctions, we have seen hammer prices reaching up to 300 euros for coins of similar condition. This suggests that there is a growing interest in well-preserved coins.

Based on these factors, an estimated maximum purchase price for this coin could be between 250 and 350 euros, considering that the condition is high and there is a history of hammer prices that supports this estimate.

Therefore, a reasonable maximum purchase price could be 300 euros.