To estimate a maximum purchase price for the coin that is going to be auctioned, we can analyze the provided data, especially previous hammer prices and the current starting price.

1. Current starting price: 250 euros.
2. Hammer price history:
- Previous hammer prices varied significantly, with some reaching up to 600 euros in past auctions.
- The average hammer price in the past has been approximately 131.21 euros, but there are cases where much higher prices have been reached, especially in higher grades.

3. Condition: No specific information is provided about the condition of the coin in the current auction, which may complicate the estimation. However, by observing the hammer prices of coins with similar conditions in the past, it can be inferred that the price may vary depending on quality.

4. Price trends:
- In previous auctions, hammer prices have exceeded the current starting price, especially for coins that had a lower starting price but reached higher hammer prices.
- For example, in auctions where the starting price was 60 euros, hammer prices reached 200 euros.

5. Estimation: Given that the starting price is 250 euros and considering that significantly higher hammer prices have been reached in the past, a reasonable estimated maximum purchase price could be between 400 and 600 euros, depending on demand and the quality of the coin in the auction.

Therefore, a reasonable estimated maximum purchase price could be 500 euros.