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

1. Current starting price: 75 euros.
2. Coin condition: 70 (MBC-), indicating an acceptable but not excellent condition.
3. Auction history:
- In 2020, the coin was auctioned with a starting price of 125 euros and sold for 300 euros, with a condition of 75.
- In 2015, the starting price was 90 euros and it sold for 160 euros, although the condition is not specified.
- In 2022, the starting price was 75 euros, estimated at 125 euros, and sold for 180 euros, with a condition of 70.

4. Average hammer price: 255 euros, indicating that, in general, coins of this reference tend to reach higher prices at auction.

5. Price trends: The general trend seems to be that coins of this reference sell above their starting price, especially in cases of higher conditions.

Given that the condition of the coin in question is 70 (MBC-), and considering the auction price history and the average hammer price, an estimated maximum purchase price could be set in a range that reflects both the condition and market interest.

Estimated maximum purchase price: It could be reasonable to consider a maximum purchase price around 180-220 euros, based on the most recent hammer price and the auction history. This would allow for a competitive offer without exceeding the market value observed in previous auctions.