To estimate a maximum purchase price for the coin in question, let's consider several factors:

1. Current starting price: 3500 euros. This is the initial price set for the auction.
2. Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in fairly good shape, but not the best possible condition.
3. Auction history: The coin has been auctioned once before, with a starting price of 2250 euros and a hammer price of 2300 euros. This suggests that interest in the coin may be moderate, as it sold close to its starting price.
4. Average starting and hammer prices: The average starting price of 2875 euros and the average hammer price of 2300 euros are also important indicators. The hammer price is significantly lower than the current starting price.

Given that the coin has a starting price of 3500 euros, which is considerably higher than the previous hammer price and the average hammer price, it is likely that buyer interest may not be high enough to reach that price.

Taking all these factors into account, an estimated maximum purchase price could be positioned between the average hammer price and a bit more, considering the condition. It might be reasonable to estimate a maximum purchase price of around 2800 to 3000 euros, as this aligns with historical interest and the condition of the coin.