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. Auction History:
- It has been auctioned 9 times in the past, with 7 successful sales. This suggests there is consistent interest in the coin.
- The average hammer price in previous auctions is 57.33 euros, which can serve as a reference.

3. Starting and Hammer Prices:
- The current starting price is 20 euros, which is significantly lower than the average hammer price.
- In previous auctions, starting prices have varied, but some have reached hammer prices of up to 110 euros.

4. Price Trends:
- In the most recent auction (2024-07-11), the coin sold for 85 euros, indicating there is potential for sale in that range.

5. Estimation Based on Condition and Previous Prices:
- Given that the condition is 75, and considering that in the past, coins of similar condition have sold for prices ranging between 40 and 110 euros, we can estimate a maximum purchase price.

Taking all these factors into account, an estimated maximum purchase price for this coin could be between 70 and 90 euros, with 85 euros being a reasonable point given the last hammer price. This allows for a margin for competition in the auction and the interest of other collectors.