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

1. Starting price: 400 euros.
2. Auction history: The coin has been auctioned 10 times and has sold on all occasions, indicating good demand.
3. Average starting price: 114.44 euros.
4. Average hammer price: 209.9 euros.
5. Previous prices: Hammer prices have varied considerably, with a maximum of 440 euros in the 2022 auction and a minimum of 24 euros in 2016.

Since there is no information about the condition of the current coin, it is difficult to make an accurate estimate. However, we can observe that in previous auctions, hammer prices have fluctuated, but the highest price (440 euros) was reached in a recent auction with a condition rating of 95.

### Analysis of previous prices:
- The highest auction (440 euros) was conducted with a condition rating of 95.
- The lowest auction (24 euros) was conducted with an unspecified condition.
- Most hammer prices are below 300 euros, but there are a couple of exceptions that exceed that figure.

### Estimation:
Given that the starting price is 400 euros and considering that the average hammer price is 209.9 euros, it is reasonable to assume that the hammer price could be in a higher range due to demand and sales history.

Estimated maximum purchase price: It could be between 300 and 450 euros, considering that the starting price is 400 euros and that there have been recent sales exceeding 400 euros. A prudent maximum purchase price could be 450 euros, given the auction history and observed demand.