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

1. Current starting price: 350 euros.
2. Coin condition: 70 (MBC-), which indicates good preservation, although it is not the best.
3. Auction history: The coin has been auctioned once before, with a starting price of 200 euros and a hammer price of 370 euros. This suggests that there is interest in the coin and that it may reach a similar or higher price in the next auction.
4. Average starting and hammer price: The average starting price is 275 euros and the average hammer price is 370 euros. This indicates that, in general, coins of this reference tend to sell well.

Given that the coin is in good condition and has shown interest in the past, an estimated maximum purchase price could be around the previous hammer price, which was 370 euros. However, since the current starting price is 350 euros, it is reasonable to consider that the maximum purchase price could be slightly higher than the previous hammer price, but not too much, to avoid overpaying.

Therefore, an estimated maximum purchase price could be approximately 400 euros. This allows for some margin for competition in the auction, considering the interest the coin has shown in the past.