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

1. Current Condition: The coin has a condition rating of 80 (MBC+). This is an important factor, as coins in better condition tend to fetch higher prices.

2. Starting Price and Average Hammer Price: The current starting price is 700 euros, and the average hammer price in previous auctions is 673.02 euros. This suggests that the starting price is aligned with the market value.

3. Sales History: The coin has been auctioned 79 times, of which it has sold 68 times. This indicates good demand and a history of successful sales.

4. Previous Prices: Looking at previous hammer prices for coins with similar conditions, we can see that they have reached hammer prices that vary, but some have exceeded 800 euros, especially in conditions of 85 or higher.

5. Recent Trends: In the most recent auctions, hammer prices have been in the range of 700 to 1100 euros, depending on the condition.

Based on these factors, an estimated maximum purchase price for this coin could be in the range of 800 to 900 euros, considering that the condition is good and there is a history of hammer prices suggesting it could reach that level.

Therefore, a reasonable maximum purchase price could be 850 euros.