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

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

2. Historical Prices: By looking at previous auction prices for coins with similar conditions, we can see that:
- In 2019, a coin with a condition of 70 was auctioned for 190 euros.
- In 2023, a coin with a condition of 75 was auctioned for 400 euros.
- In 2020, a coin with a condition of 85 was auctioned for 420 euros.

3. Average Auction Price: The average auction price for this coin is 423.4 euros, indicating that, in general, coins of this reference tend to reach high prices.

4. Starting Price and Average Starting Price: The current starting price is 175 euros, and the average starting price is 235.14 euros. This suggests that the starting price is relatively low compared to previous auction prices.

5. Recent Trends: In the most recent auctions, the auction prices have shown a trend of being higher, especially for coins with superior conditions.

Based on these factors, an estimated maximum purchase price for the coin could be in the range of 400 to 600 euros, considering that the condition is a limiting factor and that the auction price may vary depending on demand at the auction.

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