To estimate a maximum purchase price for the coin in question, we can analyze the provided data, including the auction history and the current condition of the coin.

1. Current Condition: The coin has a condition rating of 80 (MS+), indicating that it is in quite good shape. This is relevant because coins in better condition tend to fetch higher prices at auctions.

2. Price History:
- The average hammer price for similar coins in the past is 1064.44 euros.
- Previous hammer prices for coins with a similar condition (80) have been:
- 950 euros (2018)
- 730 euros (2014)
- 400 euros (2013)
- 650 euros (2016)
- The highest hammer price for a coin with a higher condition (90) was 1350 euros.

3. Starting Price: The starting price of the current auction is 800 euros, which is a reasonable starting point.

4. Sales Trends: The coin has been sold in 76.9% of past auctions, suggesting good demand.

5. Maximum Price Estimate: Given that the average hammer price is 1064.44 euros and considering that the coin's condition is 80, a hammer price in the range of 1000 to 1200 euros seems reasonable. However, since the starting price is 800 euros, it is likely that bidders will be willing to pay a bit more.

Conclusion: Based on the above analysis, an estimated maximum purchase price for this coin could be in the range of 1100 to 1300 euros. This takes into account the condition, price history, and sales trend.