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

1. Current Condition: The coin has a condition rating of 80 (MS+), indicating that it is in good condition. This generally increases its value compared to coins with lower conditions.

2. Auction History:
- The coin has been auctioned 6 times, of which it has sold 5 times. This suggests there is consistent interest in the coin.
- Previous hammer prices varied, but the highest was 65 euros in 2018, with a condition of 70.
- In more recent auctions, hammer prices have been lower, especially for coins in condition 30.

3. Starting Price and Average Price:
- The current starting price is 50 euros, which is higher than the average starting price of 33.13 euros. This may indicate that the seller has higher expectations due to the good condition of the coin.
- The average hammer price is 41 euros, which is also an indicator of what buyers are willing to pay.

4. Price Trends:
- The trend of hammer prices seems to be slightly increasing, especially for coins in better condition.

Given all this, and considering that the condition of this coin is superior to that of previous auctions that have reached higher prices, an estimated maximum purchase price could be in the range of 70 to 80 euros. This is based on the good condition and the demonstrated interest in previous auctions.

Therefore, an estimated maximum purchase price could be 75 euros.