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

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

2. Auction History:
- The average hammer price for similar coins in the past is 244 euros.
- The last auction of a coin with a similar condition (90) had a hammer price of 500 euros, suggesting that there is significant interest in high-quality coins.

3. Starting Price: The starting price is 300 euros, which may influence the final price, as buyers often consider the starting price as an indicator of the coin's value.

4. Price Trends: In previous auctions, we have seen hammer prices that varied considerably, but coins in better condition tend to reach higher prices. For example, in the 2023 auction, a coin with a condition of 85 sold for 500 euros.

Based on these factors, an estimated maximum purchase price for this coin could be in the range of 400 to 600 euros, considering its good condition and the interest shown in previous auctions. A more conservative price could be around 450 euros, while a more optimistic price could reach up to 600 euros, depending on the competition in the auction.