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

1. Condition: The coin has a condition rating of 80 (MBC+), which indicates that it is in fairly good shape, but not the best possible condition (FDC).

2. Previous auction prices: By looking at the hammer prices of coins with similar conditions (around 80-85), we can see that the hammer prices have varied, but generally have remained in a range of 480 to 750 euros.

3. Starting price and average hammer price: The current starting price is 650 euros, and the average hammer price in previous auctions is approximately 630.98 euros. This suggests that the starting price is aligned with the market value.

4. Auction trends: The coin has been auctioned 89 times, with a high sales percentage (86 out of 89). This indicates that there is consistent interest in this coin, which may influence its price.

5. Recent hammer prices: In the most recent auctions, hammer prices have been in the range of 600 to 800 euros for coins of similar condition.

Based on these factors, an estimated maximum purchase price for this coin could be around 750-800 euros. This is because, although the starting price is 650 euros, the interest in the coin and its condition suggest that it could reach a higher price at auction.