To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially considering the current condition of the coin (80 - MBC+) and previous auction prices.

1. Condition: The coin has a condition of 80 (MBC+), indicating that it is in fairly good shape, but not the best possible condition.

2. Price History:
- The average hammer price for coins with a similar condition (80) has been approximately 30 to 40 euros in several previous auctions.
- In recent auctions, hammer prices for coins with a condition of 80 have ranged from 20 to 65 euros.

3. Price Trends:
- In previous auctions, hammer prices have reached up to 85 euros for coins with a condition of 90, suggesting that there is potential for price increases for coins in lower conditions, but within a lower range.

4. Estimated Price:
- Given that the average hammer price has been 51.1 euros and considering that the condition of this coin is 80, an estimated maximum purchase price could be in the range of 60 to 80 euros, taking into account the price trend and condition.

Therefore, an estimated maximum purchase price for this coin could be 70 euros. This price reflects a balance between the price history and the current condition of the coin.