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. Auction History:
- The average hammer price for this coin in the past is 339.65 euros.
- The last auction of this coin with a similar condition (90) sold for 500 euros.
- There are examples of coins with conditions of 85 and 95 that have sold in the range of 240 to 650 euros.

3. Starting Price: The current starting price is 325 euros, which is below the average hammer price.

4. Price Trends: Observing previous hammer prices, it seems there is a trend for coins in good condition (like the one with a condition of 90) to sell above the starting price.

Based on these factors, an estimated maximum purchase price could be in the range of 500 to 600 euros, as this is a range that has been reached in previous auctions for coins of similar condition.

Therefore, a reasonable maximum purchase price could be 550 euros.