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. Current Starting Price and Previous Prices: The current starting price is 400 euros. In previous auctions, we have seen hammer prices that varied significantly, but there are examples of hammer prices exceeding 400 euros, especially for coins in similar or better conditions.

3. Price Trends: Looking at previous hammer prices, there are several cases where coins with similar conditions have reached hammer prices of 320 euros, 360 euros, and even up to 1000 euros in exceptional conditions. However, the average hammer price for coins of similar condition seems to be around 204.53 euros.

4. Demand and Supply: The coin has been auctioned 45 times, of which 40 have been sold. This suggests that there is a consistent interest in this coin, which may increase its value at auction.

5. Estimated Price Analysis: The estimated hammer price for this coin is 150 euros, but considering the condition and the interest in the coin, it is reasonable to expect that the actual hammer price will be higher.

Based on these factors, an estimated maximum purchase price could be in the range of 400 to 600 euros, considering that the starting price is 400 euros and that there are precedents for higher hammer prices in similar conditions. A reasonable maximum purchase price could be 550 euros.