To estimate a maximum purchase price for the coin in question, we can analyze the provided data:

1. Current starting price: 250 euros.
2. Average starting price in previous auctions: 417.39 euros.
3. Average hammer price in previous auctions: 506.76 euros.
4. Hammer price history: Hammer prices have varied, but many have been in the range of 460 to 810 euros, with a notable hammer price of 700 euros on some occasions.

Since the condition of the current coin is not specified, but considering that in the past, coins with similar condition (condition value 95) have had hammer prices ranging between 460 and 810 euros, we can make an estimation.

### Estimation of the maximum purchase price:
- Based on the average hammer price: 506.76 euros.
- Considering the range of previous hammer prices: We could consider a maximum purchase price in the high range, given that the starting price is relatively low (250 euros).

Therefore, an estimated maximum purchase price could be between 500 and 600 euros, taking into account that the highest hammer price in the past has been 810 euros, but also considering that the current starting price is 250 euros.

### Conclusion:
Estimated maximum purchase price: 600 euros.