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

1. Current starting price: 450 euros.
2. Previous hammer prices:
- Hammer prices have varied, ranging from 240 euros to 750 euros in previous auctions.
- The most recent hammer prices (2024) include 525 euros and 700 euros, indicating growing interest in the coin.

3. Average hammer price: 310.78 euros, suggesting that, in general, coins of this reference sell for a price lower than the current starting price.

4. Condition: There is no information on the condition of this coin, which may affect its value. However, the highest hammer prices in the past have been for coins in good condition.

5. Recent trends: Hammer prices have shown an increase in recent years, which could indicate a rise in demand.

Given that the starting price is 450 euros and considering previous hammer prices, an estimated maximum purchase price could be in the range of 500 to 600 euros, taking into account that interest in the coin seems to be increasing and that recent hammer prices have been higher.

Therefore, an estimated maximum purchase price could be 550 euros.