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

1. Starting Price: 1000 euros. This is the initial price set for the auction.
2. Condition: The coin has a condition rating of 90 (EF), indicating that it is in very good shape. This generally increases its value compared to coins with lower conditions.
3. Auction History: The coin has been auctioned 2 times in the past and has sold on both occasions. This suggests that there is interest in the coin and that it has an active market.
4. Previous Prices: In the previous auction, the coin was offered with a starting price of 500 euros and was sold for 850 euros, indicating that the market is willing to pay more than the starting price.

Given that the average hammer price for similar coins is 1575 euros and considering that the condition of this coin is better than that of the previous auction, we can estimate that the hammer price could be higher.

Taking all these factors into account, an estimated maximum purchase price could be between 1500 and 1800 euros, depending on the competition in the auction and the interest of collectors. A price of 1800 euros could be a reasonable limit for a competitive bid, given the price history and the condition of the coin.