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 quite good shape. This generally translates to a higher price compared to coins in lower conditions.

2. Auction History:
- The average hammer price for similar coins in the past is 41.34 euros.
- In previous auctions, we have seen hammer prices that varied significantly, but there are examples of coins in similar conditions that have sold for significantly higher prices, such as 240 euros for a coin in FDC (100) condition and 86 euros in a recent auction.

3. Starting Price and Estimated Price:
- The current starting price is 12 euros, which is relatively low compared to the average hammer price.
- The estimated price for this auction is 20 euros, which also suggests potential for an increase in the hammer price.

4. Recent Trends: In the most recent auctions, hammer prices have shown an increase, especially for coins in higher condition grades.

Taking all these factors into account, an estimated maximum purchase price for this coin could be in the range of 70 to 100 euros. This range considers the good condition of the coin, the auction price history, and the trend of increasing prices in recent auctions.