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

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

2. Auction History:
- In the past, the coin has been auctioned 7 times, of which it has sold 6 times. This suggests there is consistent interest in the coin.
- Previous hammer prices for coins with a similar condition (80) have been 1100 euros (2018) and 1600 euros (2013). This indicates that the hammer price can be quite high for coins in good condition.

3. Average Hammer Price: The average hammer price for this coin is 922 euros, which is also an important indicator to consider.

4. Starting Price: The current starting price is 300 euros, which is significantly lower than previous hammer prices.

5. Price Trends: Given that the average starting price is 433.33 euros and the average hammer price is 922 euros, there is a considerable margin between the starting price and the hammer price.

Based on these factors, an estimated maximum purchase price could be positioned in a range between the average hammer price and the higher hammer prices observed in the past.

Estimated Maximum Purchase Price:

We could consider a maximum purchase price of around 1100 to 1300 euros, as this range aligns with previous hammer prices for coins in similar conditions and the demonstrated interest in past auctions.

Therefore, a reasonable maximum purchase price could be 1200 euros.