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

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

2. Auction History:
- The average hammer price for this coin has been 493.88 euros.
- In previous auctions, hammer prices have varied, but there are recent examples where the coin has reached significantly high prices, such as 2400 euros in a 2022 auction with a condition of 95.
- The last auction in which this coin was sold with a similar condition (80) had a hammer price of 750 euros.

3. Starting Price: The current starting price is 400 euros, which is a good starting point, but given the hammer price history, the final price may be considerably higher.

4. Market Trends: Since the coin has been auctioned 34 times and all have been sold, this indicates a steady demand. Additionally, the average hammer price has been increasing in recent years.

Based on these factors, an estimated maximum purchase price could be in the range of 700 to 900 euros, considering that the most recent high hammer price was 750 euros and that the coin's condition is good. This also takes into account the possibility that bidders may be willing to pay more in a competitive auction.