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. Current Listing Price and Previous Prices: The current listing price is 800 euros. The average hammer price in previous auctions is 1035.94 euros, suggesting that coins of this reference tend to sell for above their listing price.

3. Historical Trends: Looking at the hammer prices from previous auctions, there are examples of similar coins that have sold for significantly higher prices, especially those with similar or better conditions. For instance, in a recent auction, a coin with a condition of 75 sold for 3900 euros, indicating a strong market for coins of this reference.

4. Price Estimates: The estimated price for this auction is 1700 euros, which also suggests that bidders are willing to pay more than the listing price.

Considering all these factors, an estimated maximum purchase price could be around 1500-1700 euros, as this aligns with previous price trends and the condition of the coin. However, it is important to remember that the final price may vary depending on the competition in the auction and the interest of collectors.