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. Current Starting Price and Previous Prices: The current starting price is 375 euros. In previous auctions, hammer prices for coins with similar conditions (90 and 85) have varied, but many have reached or exceeded 300 euros. For example, in recent auctions, coins with a condition of 90 have reached hammer prices of up to 420 euros.

3. Price Trends: Looking at the hammer prices of similar coins in the past, the average hammer price has been approximately 276.88 euros, but there are examples where they have sold for over 400 euros, especially in conditions of 90 or higher.

4. Sale Expectations: Given that there are 2 auctions scheduled in the coming days, this may increase competition and, therefore, the hammer price.

Based on these factors, an estimated maximum purchase price for this coin could be between 400 and 450 euros, considering that the condition is good and there is potential interest in the auction. This also takes into account the price trend in recent auctions and the current starting price.