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

1. Current and previous prices: The current starting price is 5000 euros, and the average starting price in previous auctions is 5937.5 euros. This suggests that the current starting price is reasonable compared to the historical data.

2. Previous hammer prices: Previous hammer prices vary, but the average hammer price is 8780 euros. This indicates that, generally, coins of this reference tend to sell for a price higher than the starting price.

3. Condition: There is no information about the condition of this coin, which may complicate the estimation. However, in previous auctions, coins with conditions ranging from 75 to 90 have had hammer prices ranging from 4200 to 10500 euros.

4. Sales trends: Out of the 9 times it has been auctioned, it has sold 5 times, indicating moderate interest in the coin.

5. Previous estimates: Estimated prices in previous auctions have been significantly higher than the starting prices, suggesting that buyers are willing to pay more.

Based on these points, an estimated maximum purchase price could be positioned in a range between the average hammer price (8780 euros) and the highest hammer price in the past (10500 euros).

Therefore, a reasonable estimated maximum purchase price could be between 9000 and 10500 euros, depending on the competition in the auction and the interest of collectors.