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

2. Auction History:
- The average hammer price in the past has been 45 euros.
- There is a notable hammer price of 137.19 euros in 2011 for a coin with a condition of 107, which is significantly higher than the current condition.
- In recent auctions, hammer prices have varied, but many have been in the range of 20 to 55 euros for similar conditions.

3. Starting Price and Average Starting Price: The current starting price is 30 euros, and the average starting price in the past has been 28.85 euros. This suggests that the starting price is reasonable and could attract bidders.

4. Sales Trends: The coin has been sold in 14 out of 21 auctions, indicating consistent interest in it.

Based on these factors, an estimated maximum purchase price could be in the range of 60 to 80 euros. This is based on the current condition and the auction price history, taking into account that interest in the coin may vary depending on demand at the auction.

Therefore, a reasonable maximum purchase price could be 70 euros.