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), which indicates that it is in quite good shape. This generally translates to a higher price compared to coins in lower conditions.

2. Starting Price and Previous Prices: The starting price is 425 euros. In previous auctions, coins with similar conditions have had hammer prices that vary, but many have exceeded 300 euros. For example, in recent auctions, coins with a condition of 90 have reached hammer prices of up to 400 euros or more.

3. Price Trends: By observing the hammer prices of coins with similar conditions in the past, it can be noted that the hammer price has been increasing, especially in recent years. This suggests that the demand for coins in good condition is growing.

4. Average Hammer Price: The average hammer price for similar coins is approximately 290.62 euros, but since this coin has a better condition, it is reasonable to expect that the hammer price will be above this average.

5. Sales Expectations: 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 between 450 and 500 euros. This is based on the condition, market price trends, and the current starting price.