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

1. Current starting price: 900 euros.
2. Average hammer price in previous auctions: 1437 euros.
3. Auction history: The coin has been auctioned 10 times and has sold in all of them, indicating good demand.
4. Previous hammer prices: The hammer prices have varied, but there are examples of sales exceeding 1000 euros, even reaching 1500 euros on some occasions.

Since there is no information about the current condition of the coin, it is difficult to make an accurate estimate. However, we can consider the following points:

- The average hammer price (1437 euros) suggests that buyers are willing to pay a price higher than the starting price.
- The trend of hammer prices in the past shows that, in general, prices have been quite high, especially in recent auctions.

Based on this information, an estimated maximum purchase price could be positioned in a range between the average hammer price and a bit more, considering that the starting price is 900 euros.

Therefore, an estimated maximum purchase price could be approximately 1600 euros. This is based on the trend of previous hammer prices and the consistent demand for the coin.