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

1. Current Condition: The coin has a condition of 75 (MBC), which indicates that it is in quite good shape. This generally increases its value compared to coins with lower conditions.

2. Auction History:
- It has been auctioned 6 times in the past, of which 5 have sold. This suggests that there is consistent interest in the coin.
- The average hammer price in previous auctions is 27.6 euros, which provides a good reference for the current value.
- Previous hammer prices for coins with similar conditions (70) have been 24, 21, 28, and 25 euros. This suggests that the price range for coins in similar conditions is between 21 and 28 euros.

3. Starting Price and Estimated Price: The starting price is 25 euros, and the estimated price is also 25 euros. This indicates that the seller has reasonable expectations based on the sales history.

4. Market Trends: Given that the condition of this coin is better than those previously auctioned (75 versus 70), it is reasonable to assume that it could reach a higher price than the average of 27.6 euros.

Taking all these factors into account, an estimated maximum purchase price could be around 30 euros. This is based on the fact that the condition is better than the previously auctioned coins and that the interest in the coin appears to be solid.