To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current Condition: The coin has a condition of 70 (VF-). This is an important factor, as coins in better condition tend to reach higher prices.

2. Starting Price and Average Hammer Price: The starting price is 220 euros, and the average hammer price in previous auctions is 392.75 euros. This suggests that, in general, coins of this reference tend to sell for a significantly higher price than their starting price.

3. Sales History: The coin has been auctioned 78 times, of which 72 have been sold. This indicates good demand and a history of successful sales.

4. Previous Prices: By looking at previous hammer prices for coins with similar conditions, we can see that prices have varied. For example, in previous auctions, coins with conditions of 75 have reached hammer prices of up to 600 euros, while others with conditions of 85 have reached 1200 euros.

5. Recent Trends: In the most recent auctions, hammer prices have shown a trend of being higher, especially for coins in similar conditions.

Based on these factors, an estimated maximum purchase price for this coin could be in the range of 400 to 600 euros, considering that the average hammer price is 392.75 euros and that the condition of 70 is relatively good, but not exceptional.

Therefore, a reasonable maximum purchase price could be approximately 500 euros.