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

1. Current Condition: The coin has a condition rating of 85 (MBC+/EBC-), indicating that it is in quite good shape. This can positively influence its value.

2. Auction History:
- The coin has been auctioned 8 times, of which it has sold 6 times. This suggests there is consistent interest in the coin.
- The average hammer price in previous auctions is 588.33 euros, which can serve as a good indicator of market value.

3. Previous Hammer Prices:
- Previous hammer prices have varied, but there are examples of hammer prices exceeding 500 euros, even reaching up to 1100 euros in similar or better conditions.
- The most recent auction with a condition of 90 reached a hammer price of 1100 euros, suggesting that a condition of 85 could be in a similar price range, albeit slightly lower.

4. Starting Price and Average Starting Price:
- The current starting price is 500 euros, which is a reasonable starting point. However, the average starting price of 457.22 euros indicates that there may be room for negotiation.

5. Market Trends:
- Given that the coin will be auctioned in the coming days and has a history of successful sales, it is likely that interest will remain.

Based on these factors, an estimated maximum purchase price could be in the range of 600 to 800 euros, considering that the condition is good and there is a history of hammer prices supporting this estimate. A price of 700 euros could be a reasonable target, allowing for some margin for competition in the auction.