To estimate a maximum purchase price for the coin that will be auctioned, we will consider several factors, including the starting price, the auction price history, and the condition of similar coins.

1. Starting Price: 100 euros.
2. Auction Price History:
- In previous auctions, the hammer prices have varied considerably, with some reaching up to 650 euros in similar conditions.
- Most hammer prices for coins in similar condition (in the range of 70 to 90) have been between 30 and 300 euros, depending on demand and rarity.

3. Condition: There is no specific information about the condition of this coin, which may affect its value. However, considering that there have been sales of similar coins in condition ranges of 70 to 90, we can infer that the price could be in a mid-range.

4. Auction Trends: Given that it has been auctioned 1,295 times and sold 998 times, this indicates a consistent interest in the coin, which may increase its value.

5. Estimation: Based on the starting price of 100 euros and the auction price history, a reasonable maximum purchase price could be in the range of 150 to 250 euros, depending on the competition in the auction and the condition of the coin.

Therefore, an estimated maximum purchase price could be 250 euros.