To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current Condition: The coin has a condition rating of 85 (ebc-), indicating that it is in quite good shape. This is a positive factor that can increase its value.

2. Auction History:
- The coin has been auctioned 10 times and has sold on all those occasions, indicating good demand.
- The average hammer price in previous auctions is 847.5 euros, providing a solid basis for estimating the current value.
- In previous auctions, hammer prices have varied, but there are examples of hammer prices reaching up to 1100 euros (in the case of a condition rating of 90).

3. Starting Price: The current starting price is 900 euros, which is slightly higher than the previous average hammer price, but may be reasonable given the sales history.

4. Price Trends: Observing previous hammer prices, it seems there is a price range that varies depending on the condition. The last auction with a condition rating of 90 reached 1100 euros, suggesting that a condition of 85 might be in a lower range, but could still reach a competitive price.

Based on these factors, an estimated maximum purchase price for this coin could be between 950 and 1100 euros, considering that the condition is good and there is stable demand. A price of 1000 euros could be a reasonable benchmark for a maximum bid, given the price history and current condition.