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

1. Starting Price: 400 euros. This is the initial price set for the auction.
2. Auction History: The coin has been auctioned 2 times in the past and has sold on both occasions. This indicates interest in the coin and may positively influence its value.
3. Average Starting and Hammer Price: The average starting price of 255 euros and the average hammer price of 515 euros suggest that, in general, coins of this reference tend to sell for above their starting price.
4. Condition: There is no information about the condition of this coin, which may complicate the estimation. However, the previous hammer price of 130 euros for a coin with a condition value of 30 suggests that the price can vary significantly depending on the quality of the coin.
5. Previous Prices: In the previous auction, the coin sold for 130 euros, which is considerably lower than the current starting price of 400 euros.

Given that the starting price is significantly higher than the previous hammer prices, and considering that there is no information about the condition, it is prudent to be conservative in the estimation.

Taking all these factors into account, an estimated maximum purchase price could be between 300 and 350 euros, depending on the demand at the auction and the quality of the coin. This would allow for a competitive bid without exceeding the historical value of the coin.