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 of 80 (VF+), indicating that it is in quite good shape. This generally translates to a higher price compared to coins in lower conditions.

2. Previous Prices: By looking at previous auction prices, we can see that in past auctions, coins with similar conditions (such as 90 and 85) have sold for prices ranging from 64 to 290 euros. This suggests a wide range depending on demand and condition.

3. Average Hammer Price: The average hammer price for this coin is 91.45 euros, which can serve as a good reference point.

4. Starting Price and Previous Sales: The current starting price is 50 euros, and there have been 10 sales in the past, indicating interest in the coin. However, the starting price is significantly lower than the average hammer price.

5. Recent Trends: In the most recent auction, the hammer price was 120 euros for a coin with a condition of 85, suggesting there is potential for an increase in the hammer price for coins in good condition.

Taking all these factors into account, an estimated maximum purchase price for the coin with a condition of 80 (VF+) could be in the range of 90 to 120 euros, considering that interest and demand may influence the final price.

Therefore, a reasonable estimated maximum purchase price could be 100 euros.