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

2. Auction History:
- The average hammer price for similar coins in the past is 635.24 euros.
- The coin has been auctioned 23 times, of which it has sold 22 times, indicating high demand.
- In previous auctions, hammer prices have varied, but there are examples of sales reaching up to 1000 euros for coins in better condition.

3. Starting Price and Estimated Price:
- The current starting price is 600 euros, and the estimated price is 800 euros. This suggests that the seller has high expectations, but it may also indicate that there is a market willing to pay more.

4. Recent Trends: In the most recent auctions, hammer prices have been high, even reaching 1000 euros on some occasions for coins of similar or better condition.

Based on these factors, an estimated maximum purchase price could be in the range of 800 to 1000 euros, considering that the coin's condition is good and there is a history of hammer prices supporting this estimate.

Therefore, a reasonable maximum purchase price could be 900 euros.