To estimate a maximum purchase price for the coin in question, we can analyze the provided data and 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. Previous Auction Prices:
- In 2020, the coin was auctioned with a starting price of 175 euros and sold for 300 euros.
- In 2022, the starting price was 300 euros, with a final bid of 800 euros, and the condition was 75.
- In 2024, it was auctioned with a starting price of 1200 euros and a final bid of 1200 euros, with a condition of 80.

3. Average Final Bid Price: The average final bid price for this coin is 711.43 euros, indicating that, in general, buyers are willing to pay around this figure.

4. Current Starting Price: The current starting price is 250 euros, which is relatively low compared to previous final bid prices.

5. Price Trends: Observing previous final bid prices, it seems there is an upward trend in prices, especially in the more recent auctions.

Given all this, an estimated maximum purchase price could be set in a range between the average final bid price and the highest final bid observed. Considering that the current condition is 70, which is lower than the conditions of 75 and 80 from previous auctions, a reasonable maximum price could be:

Estimated maximum purchase price: 600 - 800 euros.

This is based on the fact that, although the condition is not the best, the interest in the coin seems to be high and the final bid prices have been significant in the past.