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

1. Starting Price: 4500 euros.
2. Condition: The coin is in condition 100 (MS), indicating it is in excellent state.
3. Auction History:
- In the auction on November 3, 2021, the coin was estimated at 5000 euros and sold for 4400 euros.
- In the auction on December 16, 2021, the coin was also estimated at 5000 euros, but it sold for 6500 euros, indicating an increase in interest or value of the coin at that time.

4. Average Hammer Price: 5450 euros, which is a good indicator of the current market value.

Given that the coin is in excellent condition and considering the average hammer price of 5450 euros, as well as the fact that it has had a higher hammer price in the past (6500 euros), it can be estimated that the maximum purchase price could be in a range above the average hammer price.

Estimation of the Maximum Purchase Price: It may be reasonable to consider a maximum purchase price of around 6000 to 6500 euros, given the auction history and the condition of the coin. This would allow for competitive bidding in the auction without exceeding the observed market value.