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 (MBC+). This is an important factor, as coins in better condition tend to reach higher prices.

2. Previous Prices: By observing previous auction prices for coins with similar conditions (80 and 85), we can see that auction prices have varied. For example:
- In 2021, a coin with a condition of 80 was auctioned for 260 euros.
- In 2022, another coin with a condition of 85 was auctioned for 440 euros.
- In 2023, a coin with a condition of 85 was auctioned for 380 euros.

3. Starting Price and Average Auction Price: The current starting price is 350 euros, and the average auction price in the past has been approximately 339.68 euros. This suggests that the auction price may be close to the starting price.

4. Auction Trends: The coin has been auctioned 36 times, of which it has sold 32 times. This indicates good demand and consistent interest in the coin.

5. Previous Estimates: Estimated prices in previous auctions for coins with similar conditions have ranged between 300 and 450 euros.

Based on these factors, an estimated maximum purchase price could be in the range of 400 to 500 euros, considering that the condition is good and there is a history of auction prices that supports this estimate.

Therefore, a reasonable maximum purchase price could be 450 euros.