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

1. Current starting price: 1200 euros.
2. Auction history: The coin has been auctioned 34 times, of which it has sold 25 times. This indicates a sell-through rate of 73.5%, which is quite positive.
3. Previous prices: Previous hammer prices varied significantly, but there are several examples of auctions that exceeded 1000 euros, especially in high grades (100 and 95).
4. Average hammer price: The average hammer price is 763.74 euros, suggesting that the current starting price of 1200 euros is significantly higher than the historical average.
5. Condition: There is no specific information about the condition of this coin, which may make buyers more cautious. However, the history shows that coins in good condition have reached high hammer prices.

Given that the starting price is 1200 euros and considering the auction price history, an estimated maximum purchase price could be in the range of 1500 to 1800 euros, depending on the demand at the auction and collectors' perception of the coin's condition.

Therefore, an estimated maximum purchase price could be 1600 euros. This is based on the fact that it is a price above the starting price, but still within a reasonable range considering previous hammer prices.