To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current Condition: The coin is in a condition of 90 (EF), indicating that it is in quite good shape.

2. Starting Price and Average Hammer Price: The starting price is 325 euros, and the average hammer price in previous auctions is 318.09 euros. This suggests that the hammer price tends to be close to the starting price.

3. Sales History: In the past, coins with a similar condition (around 90) have reached hammer prices that varied, but some recent examples show hammer prices of up to 400 euros for coins in similar conditions.

4. Recent Trends: Observing recent auctions, there is an increase in hammer prices for coins in good condition, which could indicate a rising trend in interest and value for these coins.

5. Comparison with Previous Prices: In previous auctions, coins with a condition of 90 have had hammer prices ranging between 350 and 400 euros.

Based on these factors, an estimated maximum purchase price for this coin could be between 400 and 450 euros, considering that interest in coins in good condition is on the rise and that the hammer price could exceed the starting price. However, it is important to keep in mind that the final price will depend on the competition in the auction and the specific demand at that moment.