To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially considering the coin's condition, which is 100 (Uncirculated), and previous auction prices.

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

2. Previous auction prices:
- In previous auctions, we have seen hammer prices of up to 50 euros for coins in condition 100.
- The average hammer price for similar coins has been 22.22 euros.

3. Starting price and estimates:
- The current starting price is 12 euros, which is reasonable given the history of starting and hammer prices.
- The estimated hammer price in previous auctions has ranged between 15 and 40 euros, with a maximum price of 50 euros in a prior auction.

4. Trends: Given that the coin has been auctioned 15 times in the past and has a successful sales history (9 out of 15), this suggests a steady demand.

Based on these factors, an estimated maximum purchase price for this coin could be in the range of 40 to 50 euros, considering its excellent condition and the history of hammer prices. Therefore, a reasonable maximum purchase price could be 45 euros.