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

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

2. Auction History:
- The average hammer price for this coin in the past has been 39.14 euros.
- The last auction of this coin with a similar condition (75) had a hammer price of 18 euros, while another with a condition of 85 sold for 82 euros.
- The trend shows that coins with better conditions tend to reach higher prices.

3. Starting Price and Previous Prices:
- The current starting price is 35 euros, which is slightly higher than the average starting price of 28.32 euros.
- Since there have been 21 sales from 26 auctions, this indicates that there is interest in the coin.

4. Estimation Based on Average Hammer Price: Given that the average hammer price is 39.14 euros and considering that the condition of the coin is better than some that have sold in the past, we can estimate that the hammer price could be in a higher range.

Taking all these factors into account, an estimated maximum purchase price for this coin could be between 45 and 55 euros. This is based on the condition, the interest shown in previous auctions, and the average hammer price.