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

1. Current Condition: The coin has a condition of 75 (MBC), which is a medium state of preservation. This suggests that its value will not be as high as that of coins in better condition.

2. Auction History:
- The coin has been auctioned 7 times in the past, of which it has sold 6 times. This indicates good demand.
- The average hammer price in previous auctions is 121.67 euros, which provides a benchmark for the coin's value.

3. Previous Prices:
- In previous auctions, hammer prices have varied, but there is a pattern where coins with a similar condition (75) have had hammer prices ranging between 80 and 220 euros.
- The highest hammer price for a coin with a condition of 75 was 220 euros, indicating that there is potential for a higher price in the future.

4. Starting Price and Average Starting Price:
- The current starting price is 90 euros, which is a reasonable price to start the auction.
- The average starting price of 91.43 euros also suggests that this is an expected range.

5. Maximum Price Estimate:
- Given that the average hammer price is 121.67 euros and considering that the condition is 75, a maximum purchase price could be positioned in a range between the average hammer price and the highest observed hammer price.
- An estimated maximum price could be around 150 euros, which is a conservative and reasonable value, taking into account the condition and auction history.

Therefore, the estimated maximum purchase price for this coin could be 150 euros.