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 (MBC+/EBC-), indicating that it is in relatively good shape. This can positively influence its price.

2. Starting Price and Average Hammer Price: The starting price is 650 euros, and the average hammer price in previous auctions is 655 euros. This suggests that the hammer price tends to be close to the starting price.

3. Sales History: The coin has been auctioned 89 times, of which it has sold 85 times. This indicates good demand and a history of successful sales.

4. Previous Prices: By looking at previous hammer prices for coins with similar conditions, we can see that prices have varied. For example, in recent auctions, coins with conditions ranging from 80 to 95 have reached hammer prices between 500 and 1300 euros, depending on the condition and demand at that time.

5. Recent Trends: In the most recent auctions, hammer prices have been in the range of 700 to 1200 euros for coins of similar condition.

Based on these factors, an estimated maximum purchase price for this coin could be in the range of 800 to 900 euros, considering that the hammer price is usually higher than the starting price and that the condition is good. However, it is important to keep in mind that the final price will depend on the competition in the auction and the specific demand at that moment.