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

1. Starting price: 350 euros.
2. Current condition: 70 (MBC-), which is an acceptable but not excellent condition.
3. Auction history:
- In 2020, a coin with a condition of 85 was auctioned with a starting price of 300 euros and a hammer price of 380 euros.
- In 2022, a coin with a condition of 70 was auctioned with a starting price of 220 euros and a hammer price of 320 euros.

4. Average hammer price: 370 euros, which indicates that, in general, coins of this reference tend to sell for above their starting price.

Given that the current condition of the coin is 70, similar to the one that sold in 2022, and considering that the starting price is 350 euros, an estimated hammer price could be in the range of 320 to 380 euros, based on the auction history.

Taking all these factors into account, an estimated maximum purchase price could be around 400 euros, as this would allow for competition with the hammer prices of previous auctions and consider the possibility that interest in the coin may increase in this auction.