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 85 (MBC+/EBC-), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Starting Price and Average Hammer Price: The current starting price is 375 euros, and the average hammer price in previous auctions is 321.21 euros. This suggests that the starting price is slightly higher than the average of what has sold in the past.

3. Sales History: The coin has been auctioned 32 times, of which it has sold 29 times. This indicates good demand and a history of successful sales.

4. Previous Prices: Looking at previous hammer prices for coins with similar conditions (85 and 80), we can see that hammer prices have varied, but there are examples of auctions reaching up to 800 euros (in the case of a condition of 100).

5. Recent Trends: In the most recent auctions, hammer prices have shown a trend of being higher, especially in higher conditions.

Given all this, an estimated maximum purchase price could be in the range of 400 to 500 euros, considering that the starting price is 375 euros and that the condition is good. This also takes into account the possibility that bidders may be willing to pay a bit more for a coin in good condition with a successful sales history.

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