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

1. Current Condition: The coin has a condition rating of 90 (EF), indicating that it is in good shape. This generally increases its value compared to coins with lower conditions.

2. Auction History:
- The average hammer price in previous auctions is 14.35 euros.
- The coin has been auctioned 29 times, of which it has sold 20 times, indicating good demand.
- Previous hammer prices varied, but there are examples of auctions reaching up to 45 euros (in 2017).

3. Starting Prices and Estimates:
- The current starting price is 10 euros, and the average starting price in the past has been 8.68 euros.
- Estimated prices in previous auctions have reached up to 40 euros.

4. Recent Trends: In recent auctions, the hammer price has been around 20-30 euros for coins of similar condition.

Based on this data, an estimated maximum purchase price could be in the range of 25 to 35 euros, considering the good condition of the coin and the auction price history. A price of 30 euros could be a reasonable target, as it falls in the middle of this range and reflects both the demand and the quality of the coin.