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 fairly good shape, but not among the best qualities (FDC).

2. Historical Prices: By looking at previous auction prices for coins with similar conditions, we can see that the auction prices for coins in MBC condition (75) have varied. For example, in previous auctions, coins with conditions ranging from 70 to 80 have reached auction prices between 30 and 95 euros.

3. Average Auction Price: The average auction price for this particular coin is 137.95 euros, but this includes coins in better conditions. For a condition of 75, it is reasonable to adjust this price downward.

4. Recent Trends: In the most recent auctions, the auction prices for coins with similar conditions have shown a range of 30 to 95 euros, suggesting that interest in coins in MBC condition remains strong, but not at the level of coins in superior conditions.

5. Starting Price: The starting price of 25 euros is a good indicator of the minimum base, but given the interest and demand, it is likely that the auction price will be significantly higher.

Based on these factors, an estimated maximum purchase price for the coin in condition 75 could be in the range of 80 to 120 euros. This reflects a balance between the quality of the coin, historical prices, and the current market trend.