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

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

2. Auction History:
- It has been auctioned 6 times in the past, of which 5 have sold. This indicates a consistent interest in the coin.
- The average hammer price in previous auctions is 50 euros, which can serve as a good indicator of market value.

3. Previous Starting and Hammer Prices:
- Starting prices have varied between 30 and 60 euros, and hammer prices have reached up to 80 euros in the past.
- In the most recent auction (2022), the starting price was 60 euros with an estimated price of 100 euros, suggesting there is potential for a higher price in the future.

4. Price Trends: Given that the average hammer price is 50 euros and considering that the condition of this coin is good, we can assume that the price could be in the upper range of previous prices.

Taking all these factors into account, an estimated maximum purchase price for this coin could be between 70 and 80 euros, given that it has reached hammer prices of up to 80 euros in the past and the condition is favorable.

Therefore, a reasonable maximum purchase price could be 75 euros.