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 indicates that it is in an acceptable state, but not of the highest quality.

2. Starting Price and Average Hammer Price: The starting price is 400 euros, and the average hammer price in previous auctions is 282.81 euros. This suggests that the starting price is relatively high compared to what has been sold in the past.

3. Sales History: The coin has been auctioned 99 times, of which it has sold 92 times. This indicates good demand and a history of successful sales.

4. Previous Prices: Looking at previous hammer prices for coins with similar conditions (70-80), prices have varied, but many have been in the range of 220 to 400 euros. The last auction with a similar condition (70) had a hammer price of 231 euros.

5. Recent Trends: In the most recent auctions, hammer prices have been in a higher range, with some reaching up to 600 euros for higher conditions.

Given all this, an estimated maximum purchase price could be set in a range between 350 and 450 euros, considering that the starting price is 400 euros and that the condition is 70. This allows for some competition in the auction but also reflects the hammer price history for similar conditions.

Therefore, a reasonable maximum purchase price could be 450 euros.