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

1. Current Condition: The coin has a condition rating of 75 (MBC), indicating that it is in fairly good shape.

2. Current Starting Price and Previous Prices: The current starting price is 100 euros. In previous auctions, the average hammer price has been 79.71 euros, suggesting that the current starting price is relatively high compared to the historical average.

3. Sales History: The coin has been auctioned 68 times, of which it has sold 62 times. This indicates good demand and a history of successful sales.

4. Previous Hammer Prices: Looking at previous hammer prices for coins with a similar condition (75), we can see that they have varied, but some have reached hammer prices of up to 110 euros under similar conditions.

5. Recent Trends: In the most recent auction, the coin sold for 140 euros with a condition of 90, indicating that there is potential for an increase in the coin's value.

Based on these factors, an estimated maximum purchase price could be between 120 and 140 euros, considering that the starting price is 100 euros and that there is a history of hammer prices suggesting that coins in similar conditions have reached higher prices.

Therefore, a reasonable maximum purchase price could be 130 euros.