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 75 (MBC), indicating an average state of preservation. This is important because the price of coins often varies significantly based on their condition.

2. Auction History:
- The average hammer price for similar coins has been 687.53 euros.
- In previous auctions, the hammer prices for coins with a similar condition (75) have varied, with the highest being 2200 euros and the lowest 340 euros.
- The last auction of a coin with a condition of 75 had a hammer price of 240 euros.

3. Starting Price: The current starting price is 350 euros, which is a reasonable starting point.

4. Sales Trends: Of the 20 times this coin has been auctioned, it has sold 16 times, indicating good demand.

5. Comparison with Previous Prices:
- In 2014, a coin with a condition of 85 sold for 532.22 euros, suggesting that the price may be higher for coins in better condition.
- In 2016, a coin with a condition of 75 sold for 340 euros, setting a precedent for the hammer price in this condition.

Taking all these factors into account, an estimated maximum purchase price for this coin could be in the range of 500 to 700 euros, considering that the average hammer price is 687.53 euros and that condition is a key factor.

Therefore, a reasonable maximum purchase price could be 650 euros.