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

1. Current starting price: 400 euros.
2. Average past starting price: 325 euros.
3. Average past hammer price: 460 euros.
4. Coin condition: 70 (MBC-), indicating good preservation.
5. Auction history: It has been auctioned once before and sold on that occasion.

Given that the coin has a condition of 70, which is quite good, and considering that the average hammer price in the past was 460 euros, this suggests that there is interest in the coin at prices close to this value.

The current starting price is 400 euros, which is reasonable given the auction history. However, since the average hammer price was 460 euros, we might consider that the maximum purchase price could be in a range close to this value.

Taking all these factors into account, an estimated maximum purchase price could be approximately 450 euros. This allows for some margin for competition in the auction, while also remaining below the previous average hammer price.