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 relatively good shape. This suggests that its value should be above that of coins with lower conditions.

2. Historical Prices: By looking at previous auction prices, we can see that coins with similar conditions have reached auction prices that vary considerably. For example:
- A coin with a condition of 95 sold for 145 euros.
- Another with a condition of 85 sold for 140 euros.
- A coin with a condition of 80 sold for 85 euros.

3. Average Auction Price: The average auction price for this coin is 111.13 euros, which is also a good indicator of the expected value.

4. Starting Price: The current starting price is 25 euros, which is quite low compared to previous auction prices.

5. Sales Trends: The coin has been auctioned 18 times, of which 15 have been sold, indicating good demand.

Based on these factors, an estimated maximum purchase price could be in the range of 120 to 150 euros, considering that the condition of 75 is quite good and that the average auction price is 111.13 euros.

Therefore, a reasonable maximum purchase price could be 135 euros.