To estimate a maximum purchase price for the coin in question, let's consider several factors:

1. Condition: The coin has a condition of 100 (MS), indicating that it is in excellent shape. This generally increases its value compared to coins with lower conditions.

2. Auction history:
- In the past, this coin has had auction prices that varied, but the highest was 1100 euros in March 2023, with a condition of 100.
- The average hammer price in previous auctions is 962.5 euros, which is also a good indicator of market value.

3. Starting price and hammer prices:
- The current starting price is 750 euros, which is slightly lower than the average starting price of 785 euros in previous auctions.
- Given that there has been interest in this coin (4 out of 5 auctions have resulted in sales), this suggests that there is demand.

4. Previous estimates:
- Previous price estimates have been as high as 1300 euros, indicating that there is potential for a higher hammer price.

Taking all these factors into account, an estimated maximum purchase price could be around 1100-1200 euros, as this is a price that has been reached in previous auctions and reflects the high condition of the coin. However, it is important to consider the competition in the auction and the willingness of other bidders to pay.