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:
- The average hammer price in previous auctions is 18.75 euros.
- The last auction where a coin with a similar condition (80) was sold was in 2024, where the starting price was 10 euros, but no hammer price was reported.
- In previous auctions, hammer prices have varied, but there are examples of hammer prices reaching up to 60 euros for coins in better condition.

3. Starting Price and Estimates:
- The current starting price is 18 euros, which is a good indicator of the auctioneers' expectations.
- The estimated price for this auction is 25 euros, suggesting that there is an expectation for the coin to sell for a higher price than the starting bid.

4. Sales Trends: The coin has been sold in 69% of the auctions it has participated in, indicating good demand.

Taking all these factors into account, an estimated maximum purchase price could be around 30-35 euros. This is based on the history of hammer prices, the condition of the coin, and the expectations of the current auction.