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), indicating that it is in fairly good shape, but not the best possible condition.

2. Auction History:
- It has been auctioned 6 times in the past, of which it has sold 5 times. This indicates a consistent interest in the coin.
- The average hammer price in previous auctions is 1120 euros, suggesting that, in general, buyers are willing to pay close to this amount.

3. Previous Prices:
- In past auctions, hammer prices have varied, but there is a hammer price of 1900 euros for a coin with a condition of 95, and 900 euros for a condition of 75. This suggests that the price can vary significantly depending on the condition.
- The lowest hammer price for a similar condition (75) was 900 euros.

4. Starting Price: The starting price is 750 euros, which is reasonable and may attract bidders.

Given that the coin's condition is 75 and considering the auction price history, an estimated maximum purchase price could be between 900 and 1200 euros. However, since the average hammer price is 1120 euros, a reasonable maximum purchase price could be:

Estimated maximum purchase price: 1100 euros.

This price reflects a balance between the current condition, interest in the coin, and previous hammer prices.