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

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

2. Previous Prices: By looking at previous auction prices for coins with similar conditions, we can see that the hammer price has varied. For example, in recent auctions, coins with conditions of 90 have reached hammer prices of up to 380 euros.

3. Starting Price and Average Hammer Price: The current starting price is 350 euros, and the average hammer price in the past has been 318.26 euros. This suggests that the starting price is reasonable and that there is potential for a higher hammer price.

4. Recent Trends: In the most recent auctions, hammer prices for coins of similar condition have been in the range of 400 to 480 euros, indicating an upward trend.

5. Supply and Demand: Given that there are 2 auctions scheduled in the coming days, this may increase competition and, therefore, the hammer price.

Taking all these factors into account, an estimated maximum purchase price for this coin could be in the range of 450 to 500 euros. This is based on the current condition, previous hammer prices, and market trends.