To estimate a maximum purchase price for the coin in question, we will 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. Current Starting Price and Previous Prices: The current starting price is 650 euros. In previous auctions, we have seen hammer prices that vary depending on the condition. For example, in recent auctions, coins with similar conditions have reached hammer prices of up to 800 euros.

3. Price Trends: The average hammer price for similar coins is 585.1 euros, suggesting that the hammer price may be in a similar range or slightly above the starting price.

4. Sales History: The coin has been auctioned 84 times, with a high sales percentage (82 out of 84). This indicates a consistent interest in this coin, which may influence the price.

5. Recent Hammer Prices: In the most recent auctions, hammer prices have been in the range of 700 to 900 euros for coins with similar conditions.

Taking all these factors into account, an estimated maximum purchase price for this coin could be between 800 and 900 euros, considering that the interest in the coin and its condition could lead to a higher than usual hammer price.

Therefore, a reasonable maximum purchase price could be 850 euros.