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

1. Starting Price: 5000 euros. This is the initial price of the auction.
2. Condition: The coin has a condition rating of 90 (EF), indicating that it is in very good shape.
3. Auction History: The coin has been auctioned 2 times in the past and has sold on both occasions. This suggests that there is demand for this coin.
4. Previous Prices: In the previous auction, the starting price was 9000 euros, with a hammer price of 11000 euros. This indicates that the market is willing to pay more than the starting price.

Given that the average hammer price in the past has been 8200 euros and considering that the condition is good, an estimated maximum purchase price could be in the range of 11000 euros, which is the highest recorded hammer price in the previous auction.

Therefore, an estimated maximum purchase price for this coin could be 11000 euros.