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 quite good shape.

2. Previous Auction Prices:
- In previous auctions, we have seen hammer prices that varied depending on the condition. For example:
- In 2022, a coin with a condition of 90 was auctioned for 1500 euros.
- In 2021, it was auctioned for 1900 euros with a condition of 90.
- In 2020, it was auctioned for 850 euros with a condition of 85.
- In 2019, it was auctioned for 600 euros with a condition of 80.

3. Price Trends:
- The average hammer price for this coin is 1080.84 euros, suggesting that, in general, buyers are willing to pay more than the starting price on many occasions.
- The coin has a starting price of 900 euros in this auction, which is a reasonable starting point.

4. Estimation of Maximum Purchase Price:
- Given that the condition is good (90) and considering the previous auction prices, a maximum purchase price could be in the range of 1500 to 1900 euros, based on previous auctions of coins with similar conditions.

Therefore, an estimated maximum purchase price for this coin could be approximately 1800 euros. This is based on the trend of previous auction prices and the current condition of the coin.