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 rating of 70 (VF-). This is an important factor, as coins in better condition tend to reach higher prices.

2. Previous Auction Prices: Looking at the auction prices of coins with a similar condition (70), we see that in the past they have sold for:
- €300 (2020)
- €460 (2019)
- €500 (2023)

The highest auction price for a condition of 70 was €500.

3. Average Auction Price: The average auction price for all auctions of this coin is €886.5, but this includes coins in better conditions.

4. Auction Trends: The coin has been auctioned 18 times, of which 16 have sold. This indicates good demand.

5. Starting Price: The starting price is €300, which suggests that the seller has moderate expectations.

Given that the coin's condition is 70 and considering the previous auction prices, an estimated maximum purchase price could be around €500-600, taking into account that the market can fluctuate and that demand may influence the final price.

Therefore, a reasonable estimated maximum purchase price would be €600.