Based on the provided data, we can conduct an analysis to estimate a maximum purchase price for the coin in question.

1. Starting price: 3000 euros.
2. Average hammer price: 9250 euros.
3. Condition of the coin: 90 (XF - Extra Fine), indicating that the coin is in very good condition.

Since the coin has had an average hammer price of 9250 euros and considering it has been sold once in the past, this suggests there is significant interest in this coin, especially given its condition.

Given that the starting price is 3000 euros, which is considerably lower than the average hammer price, this could indicate a good buying opportunity. However, the maximum price that a buyer might be willing to pay will depend on the competition in the auction and the interest from other collectors.

Taking all these factors into account, an estimated maximum purchase price could be in a range between the average hammer price and 10-20% above the starting price, considering that the condition is high and there is a sales history.

Therefore, an estimated maximum purchase price could be around 10,000 to 11,000 euros. This would allow a competitive buyer in the auction, but it should also be noted that there is a possibility that other bidders may be interested in the coin.