To estimate a maximum purchase price for the coin in question, we will consider several factors:

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 in lower conditions.

2. Sales History: By looking at previous auction prices for coins with similar conditions (around 90-95), we can see that auction prices have varied, but there are examples of auctions reaching up to 70 euros for coins in similar conditions.

3. Average Auction Price: The average auction price for this coin is 27.36 euros, providing a solid basis for estimating a maximum price.

4. Recent Trends: In the most recent auctions, the hammer prices have shown a range that can be higher, especially for coins in superior condition.

5. Starting Price: The starting price is 15 euros, suggesting that interest in the coin may be moderate, but given the sales history, it is likely that the final price will be significantly higher.

Based on these factors, an estimated maximum purchase price for the coin could be between 40 and 60 euros, considering that the condition is good and there is a history of auction prices supporting this estimate. However, to be more conservative, a maximum purchase price of 50 euros could be a good reference.