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

1. Current Condition: The coin has a condition rating of 90 (EF), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History:
- The average hammer price for similar coins is 20.91 euros.
- In previous auctions, we have seen hammer prices that vary, but some relevant examples are:
- A coin with a condition of 95 was sold for 43 euros (2023-01-31).
- Another with a condition of 90 was sold for 10 euros (2023-02-16).
- A coin with a condition of 100 was sold for 30 euros (2024-07-11).

3. Price Trends:
- The average starting price is 13.35 euros, and the current starting price is 9 euros. This suggests that the starting price is relatively low compared to the historical average.
- The coin has previously sold in a price range from 6 euros to 85 euros, depending on the condition and demand at the time of the auction.

4. Sale Expectations: Given that there are 2 auctions scheduled in the coming days, this may increase competition and, therefore, the price.

Based on these factors, an estimated maximum purchase price for this coin could be between 25 and 35 euros. This is based on the fact that the condition is good and that the price history shows that similar coins have reached higher prices in the past. However, since the starting price is relatively low, there may be opportunities to acquire it at a lower price if competition is not high.