To estimate a maximum purchase price for the coin in question, we will consider 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 with lower conditions.

2. Auction History:
- The average hammer price for similar coins in the past is 156.1 euros.
- In previous auctions, we have seen hammer prices that varied significantly, but some relevant examples are:
- In 2021, a coin with a condition of 85 was sold for 340 euros.
- In 2023, a coin with a condition of 85 was sold for 500 euros.
- In 2014, a coin with a condition of 95 was sold for 1800 euros, although this is an extreme case.

3. Starting Price: The starting price of 300 euros is a good indicator of the seller's expectations, but it does not necessarily reflect the final hammer price.

4. Recent Trends: Recent trends show that coins with similar conditions have had hammer prices exceeding 300 euros, especially in favorable market conditions.

Based on these factors, an estimated maximum purchase price for the coin in question could be between 400 and 600 euros, considering that the condition is good and there is a history of hammer prices that supports this estimate. However, it is important to keep in mind that the final price may vary depending on the competition in the auction and the interest from other buyers.