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

2. Starting Price and Average Hammer Price: The starting price is 90 euros, and the average hammer price in previous auctions is 120.49 euros. This suggests that, on average, similar coins have reached prices above the starting price.

3. Sales History: The coin has been auctioned 51 times, of which 44 have been successful sales. This indicates good demand and consistent interest in this reference.

4. Previous Prices: By looking at previous hammer prices for coins with similar conditions (80 and 85), we can see that they have reached hammer prices that vary, but some have reached 200 euros or more under similar conditions.

5. Recent Trends: In the most recent auctions, hammer prices have shown a trend of being in the range of 100 to 150 euros for similar conditions.

Based on these factors, an estimated maximum purchase price for this coin could be between 150 and 200 euros, considering that interest and demand may push the price closer to the higher levels observed in the past.

Therefore, a reasonable maximum purchase price could be 150 euros.