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 relatively good shape, but not among the best qualities.

2. Starting Price: The starting price is 120 euros, which sets a baseline for the auction.

3. Sales History:
- The average hammer price in previous auctions is 128.77 euros.
- It has been auctioned 24 times, of which 15 have sold, indicating a sales rate of 62.5%. This suggests there is interest in the coin, but also that there is a 37.5% chance it has not sold, which may influence the perception of its value.

4. Previous Prices:
- In past auctions, hammer prices have varied significantly, ranging from 60 euros to 400 euros, depending on condition and other factors.
- The last auction with a hammer price of 400 euros was notably high, but there is no information on the condition of that coin.

5. Comparison with Similar Conditions:
- Coins with similar conditions (around 80) have had hammer prices ranging from 60 to 150 euros in the past.

Based on these factors, an estimated maximum purchase price could be in the range of 130 to 150 euros. This is based on the average hammer price and the condition of the coin. However, since the starting price is 120 euros, it is reasonable to consider that a hammer price around 140 euros could be a realistic target, assuming demand remains steady.

Therefore, an estimated maximum purchase price could be 140 euros.