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

1. Current Condition: The coin has a condition rating of 75 (MBC), indicating that it is in relatively good shape, but not among the highest qualities.

2. Historical Prices: Looking at previous auction prices, we can see that the coin has reached auction prices of up to 2300 euros in higher conditions (95 condition). However, in conditions closer to the current one (75-80 condition), the auction prices have been lower, such as 550 euros in 2015 and 300 euros in 2021.

3. Starting Price and Average Hammer Price: The current starting price is 300 euros, and the average hammer price in previous auctions is 756.67 euros. This suggests that, in general, the coin tends to sell for a price higher than the starting price.

4. Auction Trends: The coin has been auctioned 11 times, of which 10 have sold. This indicates good demand and consistent interest in the coin.

5. Estimation Based on Condition: Given that the current condition is 75, and considering that in the past coins with similar conditions have reached hammer prices of around 300 to 550 euros, we can estimate that the hammer price could be in a similar range.

Taking all these factors into account, an estimated maximum purchase price for this coin could be between 500 and 700 euros, considering that the interest in the coin and the current condition could lead to a hammer price higher than the historical average. However, given the starting price of 300 euros, it is likely that the hammer price will not significantly exceed 700 euros.

Therefore, a reasonable maximum purchase price could be 700 euros.