To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially the previous auction prices and the trend of the starting and final prices.

1. Current starting price: 3000 euros.
2. Average starting price in the past: 1202.27 euros.
3. Average final price in the past: 1941.55 euros.
4. Auction history: The coin has been auctioned 12 times, of which it has sold 11 times, indicating good demand.

### Analysis of previous prices:
- In 2020, a coin with a grade of 85 sold for 1250 euros.
- In 2020, another coin with a grade of 95 sold for 1300 euros.
- In 2021, a coin with a grade of 80 sold for 1300 euros.
- In 2024, a coin with a grade of 70 sold for 1500 euros.
- In 2024, a coin with a grade of 50 sold for 3400 euros.

### Considerations:
- The grade of the current coin is not specified, making it difficult to make a direct comparison.
- However, previous final prices suggest that, depending on the grade, the final price can vary significantly.
- The trend shows that coins with better grades tend to reach higher prices.

### Estimation:
Given that the starting price is 3000 euros, and considering that the average final price in the past is 1941.55 euros, a reasonable final price could be in the range of 2000 to 3000 euros, depending on the grade.

Estimated maximum purchase price: 2500 euros.

This price is based on the trend of previous final prices and the expectation that the coin could reach a higher price if the grade is favorable.