To estimate a maximum purchase price for the coin in question, let's consider several factors:

1. Condition: The coin has a condition rating of 75 (MBC), indicating that it is in quite good shape. This generally increases its value compared to coins with lower conditions.

2. Auction history: The coin has been auctioned twice in the past, and in the last auction, it sold for 45 euros. This is an important indicator of the interest and value of the coin in the market.

3. Starting price and previous prices: The current starting price is 30 euros, and the average hammer price in previous auctions has been 45 euros. This suggests that the market is willing to pay more than the starting price.

4. Market trends: Since the coin has sold on both occasions it was auctioned, and considering that the average hammer price is 45 euros, it is reasonable to assume that interest in this coin remains strong.

Based on these factors, an estimated maximum purchase price could be around 50-55 euros. This is because, although the average hammer price is 45 euros, the good condition and interest in the coin could justify a slightly higher price.