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 70 (VF-). 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 (70 and 80), we can see that:
- In 2018, a coin with a condition of 70 was auctioned for 60 euros.
- In 2022, a coin with a condition of 70 was auctioned for 50 euros.
- In 2020, coins with a condition of 80 were auctioned between 72 and 112 euros.

3. Average Auction Price: The average auction price for this coin is 102.68 euros, indicating that, in general, coins of this reference tend to reach higher prices.

4. Starting Price and Average Starting Price: The current starting price is 40 euros, and the average starting price in the past has been 83.55 euros. This suggests that the current starting price is relatively low compared to the historical average.

5. Sales Trends: The coin has sold in 19 of the last 21 auctions, indicating good demand.

Based on these factors, an estimated maximum purchase price could be in the range of 70 to 100 euros, considering that the condition is slightly lower than that of coins that have sold for over 100 euros in the past.

Therefore, a reasonable estimated maximum purchase price could be 90 euros. This is based on the trend of previous prices and the current condition of the coin.