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

1. Condition: The coin has a condition of 100 (MS), indicating that it is in excellent shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction history:
- The average hammer price for this coin has been 11.6 euros.
- In previous auctions, hammer prices of up to 50 euros have been recorded for coins with the same condition (as in the auction on December 17, 2020).
- Most recent auctions with a condition of 100 have had hammer prices ranging between 10 and 20 euros.

3. Starting price and estimated prices:
- The current starting price is 6 euros, which is relatively low compared to previous hammer prices.
- The estimated price for this auction is 20 euros, suggesting that bidders are willing to pay more than the starting price.

4. Sales trends: Of the 58 times it has been auctioned, it has sold 44 times, indicating good demand.

Based on these factors, an estimated maximum purchase price could be in the range of 20 to 30 euros, considering that the highest recorded hammer price was 50 euros, but recent trends suggest that prices are closer to 20 euros. Therefore, a reasonable maximum purchase price could be 25 euros.