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 of 70 (MBC-). This is an important factor, as coins in better condition tend to reach higher prices.

2. Previous Prices: By observing previous auction prices for coins with similar conditions, we can see that:
- In 2018, a coin with a condition of 70 was auctioned for 110 euros.
- In 2021, a coin with a condition of 95 was auctioned for 150 euros.
- In 2024, a coin with a condition of 70 was auctioned for 45 euros.

3. Average Auction Price: The average auction price for this coin is 100.83 euros, which gives us a good reference.

4. Starting Price and Average Starting Price: The current starting price is 50 euros, and the average starting price is 76.58 euros. This suggests that interest in the coin may be moderate.

5. Auction Trends: The coin has been auctioned 13 times, of which 12 have sold. This indicates a consistent interest in the coin.

Based on these factors, an estimated maximum purchase price could be in the range of 100 to 125 euros, considering that condition is a key factor and that the highest auction price for a similar condition was 110 euros.

Therefore, a reasonable estimated maximum purchase price could be 120 euros.