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

1. Coin Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Current Listing Price and Previous Prices: The current listing price is 600 euros. In the past, we have seen auction prices that varied significantly, but there are examples of similar coins that have sold for significantly higher prices, especially those with a condition rating of 90 or above.

3. Previous Auction Prices: Looking at previous auction prices, there are examples of coins with similar conditions that have sold for prices ranging from 100 to over 1000 euros, depending on the condition and demand at the time of the auction.

4. Sales Trends: The coin has been auctioned 39 times, of which 30 have been successful sales. This suggests that there is consistent interest in this coin, which may increase its value.

5. Average Auction Price: The average auction price for similar coins is 229.86 euros, indicating that the current listing price of 600 euros is quite high compared to the average, but it may be justified by the condition and demand.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 800 to 1000 euros. This range considers the good condition of the coin, the historical interest in it, and the potential for the auction price to exceed the current listing price. However, the final price will depend on the competition in the auction and the willingness of other bidders to pay.