To estimate a maximum purchase price for the coin in question, we will consider several factors based on the provided data:

1. Starting Price: 300 euros. This is the initial price expected to be obtained at the auction.

2. Auction History: The coin has been auctioned 7 times, of which it has sold 6 times. This indicates good demand and consistent interest in the coin.

3. Average Hammer Price: 243 euros. This is the average price at which the coins have sold in the past, which can be a good indicator of the coin's real value.

4. Condition: There is no information about the condition of this coin, which may complicate the estimation. However, in previous auctions, some coins with a condition of 70 have sold for prices ranging between 26 and 30 euros, suggesting that condition may influence the price.

5. Previous Prices: In the past, hammer prices have varied significantly, from 12 euros to 460 euros. The highest price (460 euros) was recorded in an auction where the starting price was 200 euros, indicating that there is potential for this coin to reach a high price if there is enough interest.

Given that the starting price is 300 euros and considering the average hammer price of 243 euros, an estimated maximum purchase price could be set in a range above the average price, but not as high as the starting price, especially since there is no information about the condition.

Estimated Maximum Purchase Price: It may be reasonable to estimate a maximum purchase price around 350-400 euros, assuming there is sufficient interest in the coin and that condition is not a limiting factor. This allows for a margin above the starting price, but also takes into account the history of hammer prices.