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

1. Current Condition: The coin has a condition rating of 80 (MBC+). This is an important factor, as coins in better condition tend to fetch higher prices.

2. Starting Price and Average Hammer Price: The starting price is 300 euros, and the average hammer price in previous auctions is 364.61 euros. This suggests that, in general, coins of this reference tend to sell for above their starting price.

3. Sales History: The coin has been auctioned 73 times, of which 71 have been sold. This indicates high demand and good interest in this coin.

4. Previous Prices: By looking at the hammer prices of coins with similar conditions (around 80), we can see that they have reached hammer prices that vary, but some have reached up to 600 euros in similar conditions.

5. Recent Trends: In the most recent auctions, hammer prices have been quite high, reaching up to 800 euros for coins in superior conditions.

Based on these factors, an estimated maximum purchase price for this coin could be between 400 and 600 euros, considering that the condition is good and there is a history of hammer prices that supports this estimate.

Therefore, a reasonable maximum purchase price could be 550 euros.