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

1. Current Condition: The coin has a condition of 85 (ebc-), which indicates that it is in quite good shape. This generally translates to a higher price compared to coins in lower condition.

2. Auction History:
- The average hammer price in previous auctions is 724.2 euros.
- In past auctions, hammer prices have varied, with some reaching up to 1100 euros in similar conditions.
- The last auction for this coin had a hammer price of 850 euros with a condition of 95, suggesting that the price may be higher for coins in better condition.

3. Starting Price and Estimated Price:
- The current starting price is 650 euros, and the estimated price is 800 euros. This indicates that there are expectations for the coin to sell for a price higher than the starting price.

4. Price Trends:
- In recent auctions, prices have shown an upward trend, especially for coins in good condition.

Based on these factors, an estimated maximum purchase price could be around 850-900 euros. This is based on the auction price history and the current condition of the coin. However, it is important to keep in mind that the final price may vary depending on the competition in the auction and the interest from other buyers.