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 (EBC), indicating that it is in very good shape. This generally increases its value compared to coins with lower conditions.

2. Auction History:
- It has been auctioned 8 times in the past, of which it has sold 5 times. This suggests that there is moderate interest in the coin.
- The average starting price in previous auctions is 421.43 euros, while the average hammer price is 316 euros. This indicates that, on average, coins of this reference tend to sell for a price lower than the starting price.

3. Previous Prices:
- Previous hammer prices for coins with similar conditions (70-85) have ranged from 300 to 360 euros. However, the coin in question has a better condition (90), which could justify a higher price.
- The last auction had a starting price of 250 euros and a hammer price of 250 euros, suggesting that interest may have fluctuated, but the fact that the starting price was low cannot be ignored.

4. Price Trends:
- In previous auctions, hammer prices have varied, but the highest estimated price was 500 euros for a coin with a condition of 80. Given that the condition of the current coin is better, this suggests it could reach a similar or higher price.

Based on these factors, an estimated maximum purchase price for the coin in question could be between 400 and 500 euros, considering its good condition and historical interest in the coin. A price of 450 euros could be a reasonable starting point for an offer, as it falls in the middle of this range and reflects both the interest and the quality of the coin.