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

1. Current starting price: 3000 euros.
2. Auction history:
- In 2014, the coin was auctioned with a starting price of 1800 euros and sold for 4200 euros (condition 80).
- In 2018, it was auctioned with a starting price of 2000 euros and sold for 3000 euros (no condition information).
- In 2023, it was auctioned with a starting price of 1500 euros and estimated at 2500 euros (condition 75).
- In 2024, it was auctioned with a starting price of 4000 euros and sold for 9500 euros (condition 90).
- In 2024, it was auctioned with a starting price of 3000 euros and estimated at 7000 euros (no condition information).

3. Price analysis:
- The average hammer price in previous auctions is 6740 euros, indicating that, in general, coins of this reference tend to reach higher prices than their starting price.
- The condition of the coins in previous auctions varies, but those with higher condition (like 90) achieve significantly higher prices.

4. Estimation:
- Given that the current starting price is 3000 euros and considering that in previous auctions hammer prices have reached up to 9500 euros, an estimated maximum purchase price could be positioned in a range between the starting price and the average hammer price.
- Taking into account the history and the average hammer price, a reasonable maximum purchase price could be around 7000 euros, which is the estimated price from the most recent auction with a starting price of 3000 euros.

Therefore, the estimated maximum purchase price for this coin could be 7000 euros.