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

1. Current starting price: 1000 euros.
2. Auction history: The coin has been auctioned 5 times and has sold on all occasions, indicating a constant interest in the coin.
3. Average starting price: 880 euros, suggesting that the current starting price is above the historical average.
4. Average hammer price: 1740 euros, which is significantly higher than the current starting price.
5. Previous prices:
- In 2019, it was auctioned with a starting price of 1200 euros and sold for 2400 euros.
- In 2014, the starting price was 500 euros, but the hammer price was only 500 euros, indicating that there was not much interest.
- In 2013, the starting price was 900 euros and it sold for 1900 euros.
- In 2023, the starting price was 800 euros and it sold for 1200 euros, with a condition rating of 75.

Since there is no information about the condition of the current coin, it is difficult to make an accurate estimate. However, considering that the average hammer price is 1740 euros and that significant interest has been observed in previous auctions, we could estimate a maximum purchase price.

Taking into account the current starting price of 1000 euros and the auction history, a reasonable maximum purchase price could be in the range of 1800 to 2000 euros, assuming that the condition of the coin is at least acceptable and that interest in the coin remains.

Therefore, an estimated maximum purchase price could be 2000 euros.