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

1. Current Condition: The coin has a condition of 75 (MBC), which indicates that it is in quite good shape. This is important because coins in better condition tend to fetch higher prices.

2. Auction History:
- The average hammer price in previous auctions is 24.47 euros.
- In past auctions, hammer prices have been recorded as high as 90 euros (for a condition of 85) and lower prices in similar conditions (such as 15-25 euros for conditions of 70-75).

3. Price Trends:
- The coin has a starting price of 15 euros in the current auction, which is a good starting point.
- In previous auctions, hammer prices have varied, but overall, prices have been increasing, especially for coins in good condition.

4. Comparison with Previous Prices:
- In the most recent auction with a condition of 75, the hammer price was 15 euros. However, in other auctions with similar conditions, hammer prices have reached up to 25 euros.

Based on these factors, an estimated maximum purchase price for this coin could be between 25 and 35 euros, considering that the condition is good and that the price history shows that similar coins have reached higher prices in the past.

Therefore, a reasonable maximum purchase price could be 30 euros.