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

1. Current Condition: The coin has a condition rating of 90 (EF), indicating that it is in quite good shape.

2. Historical Prices: By looking at previous auction prices for coins with similar conditions, we can see that auction prices have varied. For example, in recent auctions, coins with condition ratings of 90 have reached hammer prices of up to 400 euros.

3. Starting Price and Average Hammer Price: The current starting price is 325 euros, and the average hammer price in the past has been 283.35 euros. This suggests that the starting price is reasonable and could attract bidders.

4. Recent Trends: In the most recent auctions, hammer prices have shown an upward trend, with some reaching up to 450 euros for similar conditions.

Based on these factors, an estimated maximum purchase price for this coin could be between 400 and 450 euros, considering that interest in well-preserved coins may lead to competition among bidders. Therefore, a reasonable maximum purchase price could be approximately 450 euros.