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 good shape. This is a positive factor that can increase its value.

2. Auction History:
- The coin has been auctioned 8 times and has sold on all occasions, indicating good demand.
- Previous hammer prices have varied, but there are examples of hammer prices exceeding 1000 euros, especially for coins with similar conditions (95).

3. Starting Price and Average Price:
- The current starting price is 900 euros, which is higher than the average starting price of 711.25 euros. This suggests that the seller has high expectations for this auction.
- The average hammer price is 785.71 euros, indicating that, on average, coins of this reference have sold below their starting price.

4. Price Trends:
- In previous auctions, hammer prices have varied significantly, with some reaching up to 1600 euros. This suggests that there is potential for this coin to reach a higher price, especially if demand is strong.

5. Proximity of Other Auctions: There are 2 auctions scheduled in the coming days, which could influence competition and interest in the coin.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 1200 to 1500 euros. This is based on the hammer price history for coins of similar condition and the good demand observed in previous auctions. However, the final price will depend on the competition in the auction and the interest from collectors.