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 in lower condition.

2. Auction History:
- The average hammer price for similar coins in the past is €2380.79.
- The coin has been auctioned 36 times, of which it has sold 26 times, indicating good demand.
- Previous hammer prices for coins with a condition rating of 90 have reached up to €5194.72.

3. Starting Price: The current starting price is €400, which is significantly lower than the average hammer price.

4. Price Trends: Observing the hammer prices of coins with similar conditions, it can be seen that prices have fluctuated, but generally, coins in good condition tend to reach higher prices.

Based on these factors, an estimated maximum purchase price could be in the range of €2000 to €3000, considering that the average hammer price is €2380.79 and that the coin's condition is good. However, given the history of higher hammer prices, a maximum purchase price could reasonably be estimated at €3000.