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

1. Current Condition: The coin has a condition rating of 75 (MBC), indicating that it is in fairly good shape, but not the best possible condition.

2. Historical Prices: By looking at previous auction prices for coins with a similar condition (75), we can see that they have reached auction prices that vary, but generally fall within a range of 51 to 220 euros.

3. Average Auction Price: The average auction price for this coin is 122.95 euros, which can serve as a good indicator of market value.

4. Current Starting Price: The starting price is 40 euros, which is relatively low compared to previous auction prices.

5. Auction Trends: The coin has been auctioned 26 times, of which 21 have been sold. This indicates a consistent interest in the coin, which may influence its price.

Given all this, an estimated maximum purchase price could be in the range of 150 to 200 euros, considering that the condition is good and that previous auction prices have reached higher figures. However, since the starting price is 40 euros, it is likely that the final auction price will not significantly exceed the average auction price of 122.95 euros.

Therefore, a reasonable maximum purchase price could be 180 euros.