To estimate a maximum purchase price for the coin in question, we can analyze 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 value compared to coins in lower condition.

2. Auction history:
- The average hammer price in previous auctions is 38.67 euros.
- In the past, hammer prices have varied, but there are examples of auctions reaching up to 85 euros (in 2011) and more recent ones ranging between 20 and 28 euros.

3. Price trends:
- The coin has a starting price of 30 euros in this auction, which is consistent with the average starting price of 30.25 euros.
- The condition rating of 90 suggests that it could reach a higher price than average, especially when compared to lower condition coins that have fetched lower hammer prices.

4. Analysis of previous prices:
- In previous auctions, coins with a similar condition (90) have reached hammer prices of 25 euros (2014) and 60.31 euros (2016). This suggests that the price range can be wide, but the condition is a key factor.

Based on these points, an estimated maximum purchase price for this coin could be in the range of 60 to 80 euros, considering that the condition is good and that the price history shows it has reached higher values in the past.

Therefore, a reasonable maximum purchase price could be 70 euros.