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 (Uncirculated), indicating that it is in excellent condition. This generally increases its value compared to coins with lower conditions.

2. Auction History:
- The average hammer price in previous auctions is 60.9 euros.
- In past auctions, hammer prices have varied significantly, with a maximum hammer price of 220 euros in a recent auction (2024-09-19) for a coin with a condition rating of 95.

3. Starting Price and Estimated Prices:
- The current starting price is 12 euros, and the average starting price in the past has been 20.73 euros.
- The estimated price in previous auctions has been up to 150 euros.

4. Sales Trends: The coin has been sold in 10 out of the last 12 auctions, indicating good demand.

Based on these factors, and considering that the coin's condition is high, an estimated maximum purchase price could be in the range of 150 to 220 euros, given that the highest recorded hammer price was 220 euros and the average hammer price is 60.9 euros.

Therefore, a reasonable estimated maximum purchase price could be 200 euros. This allows for some margin for competition in the auction, given the interest and quality of the coin.