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

1. Coin Condition: The coin has a condition rating of 90 (EBC), 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 has been 44.08 euros.
- In previous auctions, coins with a similar condition (90) have reached hammer prices that varied, but some have gone up to 48 euros or more under similar conditions.

3. Starting Price: The starting price is 15 euros, suggesting that there is considerable room for the final price to be higher.

4. Price Trends: By observing previous hammer prices for coins with a condition of 90, it can be noted that the price range can vary, but it is reasonable to expect that a coin in this condition will reach a hammer price above the average.

Based on these factors, an estimated maximum purchase price for this coin could be between 60 and 80 euros, considering that the condition is good and there is a price history that supports this estimate.

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