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

1. Current Condition: The coin has a condition of 90 (EF), which indicates that it is in good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Previous Prices: By observing previous auction prices for coins with similar conditions, we can see that:
- In 2020, a coin with a condition of 80 was auctioned for 1300 euros.
- In 2019, a coin with a condition of 85 did not sell, but had an estimated price of 3000 euros.
- In 2022, a coin with a condition of 75 was auctioned for 1300 euros.
- In 2024, coins with a condition of 80 were auctioned for 1300 and 1800 euros.

3. Average Auction Price: The average auction price for this coin is 1353.13 euros, which is also a good indicator of market value.

4. Starting Price: The current starting price is 380 euros, which is significantly lower than previous auction prices.

Given that the condition of the coin is quite good (90), and considering previous auction prices and the average auction price, an estimated maximum purchase price could be in the range of 1300 to 1800 euros, depending on the competition in the auction and the interest of collectors.

Therefore, a reasonable estimated maximum purchase price could be 1500 euros. This is based on the trend of previous prices and the current condition of the coin.