To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially the previous auction prices and the current condition of the coin.

1. Current Condition: The coin has a condition of 90 (EF), indicating that it is in good shape, but not the best possible condition.

2. Previous Auction Prices:
- In previous auctions, we have seen hammer prices that vary depending on the condition. For example:
- A coin with a condition of 90 sold for 1400 euros in 2018 and 2800 euros in 2022.
- Another with a condition of 85 sold for 1800 euros in 2023.
- A coin with a condition of 95 has sold between 1050 and 1800 euros.

3. Average Hammer Price: The average hammer price for this coin is 1564.71 euros, which gives us a good reference.

4. Starting Price: The starting price is 1200 euros, which is reasonable given the price history.

5. Trends: Noting that coins with similar conditions have reached hammer prices of up to 2800 euros, we can consider that the hammer price may be significantly higher than the starting price.

Based on this data, an estimated maximum purchase price for this coin could be between 1800 and 2200 euros, considering that the condition is good and there is a price history that supports this estimate.

Therefore, a reasonable maximum purchase price could be 2000 euros.