To estimate a maximum purchase price for the coin in question, we can analyze the provided data and consider several factors:

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

2. Auction History:
- The average hammer price for coins of this reference is 574.1 euros, suggesting that, in general, buyers are willing to pay significantly more than the starting price.
- In previous auctions, we have seen hammer prices vary, but some have reached very high figures, such as 1800 euros in 2022 and 800 euros in 2023.

3. Starting Price and Average Starting Price:
- The current starting price is 300 euros, which is slightly higher than the average starting price of 226.67 euros. This may indicate that the seller is confident that the coin will reach a higher price.

4. Price Trends:
- Observing previous hammer prices, there is a trend for coins in good condition (such as 90 and 95) to sell for much higher prices than their starting price.

Based on these factors, an estimated maximum purchase price could be in the range of 700 to 900 euros, considering that the coin is in good condition and that the auction history shows that prices can be quite high.

Therefore, a reasonable maximum purchase price could be 800 euros.