To estimate a maximum purchase price for the coin in question, let's consider the following factors:

1. Starting Price: 200 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. This can increase its value compared to coins in lower condition.
3. Auction History:
- It has been auctioned 2 times in the past, of which it sold 1 time and did not sell 1 time.
- The average starting price in previous auctions was 160 euros, and the average hammer price was 220 euros.
- In the December 2020 auction, the starting price was 120 euros and the hammer price was 220 euros.

Given that the average hammer price in the past has been 220 euros and considering that the condition of the coin is high (90), it is reasonable to think that the hammer price could be in a similar range or even higher, depending on the interest of collectors.

Taking all these factors into account, an estimated maximum purchase price could be around 250-270 euros, as this reflects both historical interest and the good condition of the coin. However, it is important to remember that the final price will depend on the competition in the auction and the interest of the bidders.