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

1. Condition: The coin has a condition rating of 80 (MBC+), which is an acceptable level, but not the highest. This may influence the price, as coins in better condition tend to reach higher prices.

2. Auction History:
- The average hammer price in previous auctions for coins with a similar condition (80) has been approximately 950 to 1700 euros, depending on the auction and demand.
- The average hammer price for this particular coin has been 1091.83 euros.

3. Starting Price and Estimates:
- The current starting price is 800 euros, which is reasonable given the price history.
- The estimated price for the current auction is 800 euros, suggesting that the auctioneers expect moderate interest.

4. Price Trends:
- In previous auctions, the hammer price has varied, but it has reached up to 1700 euros on one occasion. This indicates that there is potential for the price to rise if there is enough interest.

5. Number of Auctions and Sales:
- The coin has been auctioned 7 times, of which 6 have sold. This suggests that there is consistent interest in the coin.

Based on these factors, an estimated maximum purchase price could be in the range of 1100 to 1300 euros, considering that the average hammer price has been 1091.83 euros and that there is potential for the price to rise if there is competition in the auction. However, given that the condition is 80, it is wise not to exceed 1300 euros to avoid overpaying.

Therefore, a reasonable maximum purchase price could be 1300 euros.