To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current Condition: The coin has a condition rating of 75 (MBC), indicating that it is in relatively good shape, but not among the highest qualities.

2. Auction History:
- The average hammer price in previous auctions is 393.36 euros.
- It has been auctioned 11 times, and all have been sold, indicating good demand.
- Previous hammer prices varied, but there are examples of auctions reaching up to 800 euros (as in 2016).

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

4. Price Trends: Observing previous hammer prices, it seems there is a considerable range, with some auctions reaching high prices for better conditions.

Given that the condition of this coin is 75 (MBC), and considering the average hammer price and auction history, an estimated maximum purchase price could be around 450-500 euros. This is based on the trend of previous prices and the current condition.

Therefore, a reasonable maximum purchase price could be 500 euros.