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

1. Starting price: 300 euros.
2. Current condition: 70 (MBC-), which is a fairly good condition, although not the best.
3. Auction history: The coin has been auctioned 8 times, of which it has sold 7 times. This indicates good demand.
4. Average hammer price: 259.29 euros, which is a good indicator of the coin's real market value.
5. Previous prices:
- In 2015, it sold for 320 euros with a starting price of 300 euros.
- In 2021, it sold for 280 euros with an estimated price of 150 euros, indicating that demand may have increased.
- In 2022, the hammer price was 320 euros with a condition of 70.
- In 2024, it sold for 320 euros with a condition of 70.

Given that the coin's condition is 70 and considering the previous hammer prices, an estimated maximum purchase price could be in a range between the average hammer price and the highest recorded price.

Taking all this into account, a reasonable maximum purchase price could be approximately 320 euros. This is based on the highest recorded hammer price for a similar condition and the trend of prices in previous auctions.