To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially the coin's condition and previous auction prices.

1. Current Condition: The coin has a condition of 70 (VF-). This indicates that it is in relatively good shape, but not of the highest quality (UNC).

2. Previous Auction Prices: By looking at the auction prices of coins with a similar condition (70), we can see that the auction prices have varied. For example:
- In the auction on 2020-12-15, a coin with a condition of 70 sold for 50 euros.
- In other auctions, the auction prices for similar conditions have ranged between 36 and 85 euros.

3. Average Auction Price: The average auction price for this coin is 79.63 euros, suggesting that, in general, coins of this reference tend to sell for relatively high prices.

4. Price Trends: It is also important to consider that the current starting price is 12 euros, which is quite low compared to the average auction price. This could indicate a good buying opportunity.

5. Final Estimate: Given that the condition is 70 and considering previous auction prices, an estimated maximum purchase price could be in the range of 70 to 90 euros. This is based on the fact that, although the condition is not the highest, the price history suggests it could reach a higher price at auction.

Therefore, an estimated maximum purchase price for this coin could be 85 euros.