Given that the coin has a starting price of 1000 euros and has had an average hammer price of 2400 euros in the past, we can make some estimates.

1. Starting price: 1000 euros.
2. Average hammer price: 2400 euros.
3. Auction history: It has been auctioned once and sold on that occasion, indicating that there is interest in the coin.

Since there is no information about the condition of the coin, it is difficult to make an accurate estimate. However, considering that the average hammer price is significantly higher than the starting price, and that the coin has sold in the past, we could estimate a maximum purchase price.

A reasonable approach would be to consider a range between the starting price and the average hammer price. We could estimate a maximum purchase price around 2400 euros, which is the average hammer price, but since there is no information about the condition, we might want to be a bit more conservative.

Therefore, an estimated maximum purchase price could be approximately 2000 to 2400 euros. This allows for a margin of uncertainty regarding the condition of the coin.