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

2. Auction History:
- The average hammer price for similar coins in the past is 285.36 euros.
- The average starting price is 239.71 euros.
- In previous auctions, coins with a similar condition (70) have reached hammer prices of up to 380 euros.

3. Price Trends:
- In the most recent auction of a coin with a condition of 70, the hammer price was 360 euros.
- The 2020 auction with a condition of 70 had a hammer price of 235 euros, indicating that the market may be willing to pay more for coins in better condition.

4. Current Starting Price: The starting price is 350 euros, suggesting that the seller has high expectations for this auction.

Based on these factors, an estimated maximum purchase price could be in the range of 360 to 400 euros, considering that the highest hammer price for a similar condition was 380 euros and that the starting price is 350 euros.

Therefore, a reasonable maximum purchase price could be 400 euros.