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

1. Condition: The coin has a condition rating of 100 (MS), indicating that it is in excellent condition. This generally translates to a higher market value.

2. Auction History:
- The average hammer price in previous auctions is 47 euros.
- In past auctions, hammer prices have reached up to 125 euros for coins with a similar condition (100) and under favorable auction conditions.

3. Starting Price: The current starting price is 40 euros, which is a good starting point, but given the history of hammer prices, it is likely that the final price will be significantly higher.

4. Sales Trends: The coin has been sold in 25 out of 28 auctions, indicating good demand and consistent interest in the coin.

5. Comparison with Previous Prices: In previous auctions, hammer prices for coins with conditions ranging from 90 to 100 have varied, but the highest range has been 125 euros.

Taking all these factors into account, an estimated maximum purchase price for this coin could be around 100-120 euros, given its condition and the demonstrated interest in previous auctions. This would allow for competitive bidding in the market without exceeding the historical hammer value for similar coins.