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: 300 euros.
2. Auction history:
- In 2013, the coin was auctioned with a starting price of 250 euros and sold for 340 euros, with a condition of 70 (MBC-).
- In 2020, the starting price was 260 euros, with a final bid of 263 euros, but the condition is not specified.

3. Average final bid price: 301.5 euros, indicating that, in general, coins of this reference tend to sell close to this price.

4. Current condition: 70 (MBC-), which is an acceptable condition and similar to that of the 2013 auction.

Given that the coin has a history of final bids exceeding the starting price and considering that the condition is the same as in the 2013 auction, it can be inferred that interest in this coin could be high.

Estimated maximum purchase price:
- Based on the previous highest bid (340 euros) and the average final bid price (301.5 euros), a reasonable maximum purchase price could be in the range of 320 to 350 euros, considering that the starting price is 300 euros and there is potential interest in the auction.

Therefore, an estimated maximum purchase price could be 340 euros.