To estimate a maximum purchase price for the coin that will be auctioned, we will consider several factors, including the starting price, the condition of the coin, and the hammer prices from previous auctions of coins with similar conditions.

### Relevant Data:
- Starting Price: 400 euros
- Condition of this Coin: 80 (MBC+)
- Previous Prices for this Coin:
- In previous auctions, coins with a condition of 80 have had hammer prices ranging from 200 to 400 euros, with an average hammer price of around 320 euros.

### Analysis:
1. Condition: A condition of 80 (MBC+) is good, but not the highest. This suggests that the hammer price should not be excessively high.
2. Starting Price: The starting price of 400 euros is somewhat high compared to previous hammer prices for coins of similar condition.
3. Price Trends: Looking at previous hammer prices, it seems that the price range for coins with a condition of 80 has been approximately 275 to 400 euros.

### Estimation of Maximum Purchase Price:
Given that the starting price is 400 euros and considering that the average hammer price for coins of similar condition is around 320 euros, a reasonable maximum purchase price could be slightly higher than the average, but not as high as the starting price.

Estimated Maximum Purchase Price: 350 euros.

This price reflects a balance between the condition of the coin and previous hammer prices, allowing for a potential competitive bid without exceeding the observed market value.