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

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

2. Auction History:
- The average hammer price for similar coins has been 669.28 euros.
- In the past, hammer prices have varied significantly, ranging from 65 euros to over 3800 euros, depending on the condition and demand at the time of the auction.

3. Starting Price: The starting price is 500 euros, which may indicate the seller's expectations regarding the coin's value.

4. Recent Trends: In the most recent auctions, hammer prices have exceeded the starting price, suggesting that there is interest in the coin.

5. Comparison with Previous Prices:
- In previous auctions, coins with a similar condition have reached hammer prices ranging from 350 to 1500 euros, depending on demand and other factors.

Taking all these factors into account, an estimated maximum purchase price for this coin could be in the range of 800 to 1200 euros. This range considers the current condition, the auction price history, and the starting price. However, the final price will depend on the competition in the auction and the interest of collectors at that time.