To estimate a maximum purchase price for the coin in question, we can analyze the provided data and consider several factors:

1. Current Condition: The coin has a condition of 80 (MBC+), which is quite good. In the past, coins with a similar condition have reached auction prices ranging from 2250 to 3300 euros.

2. Previous Auction Prices: The previous auction prices for coins with similar conditions are:
- 2600 euros (2019)
- 2500 euros (2018)
- 2250 euros (2018)
- 3300 euros (2015)
- 2450 euros (2014)

3. Average Auction Price: The average auction price for previous sales is 2500 euros, indicating that this is a good reference point.

4. Starting Price: The current starting price is 1900 euros, which is reasonable compared to previous auction prices.

5. Auction Trends: Since the coin has been sold on all previous occasions and there have been no failed sale attempts, this suggests a steady demand.

Based on these factors, an estimated maximum purchase price could be in the range of 2500 to 3000 euros, considering that the average auction price is 2500 euros and higher prices have been reached in previous occasions.

Therefore, a reasonable estimated maximum purchase price could be 2800 euros. This allows for some margin for competition in the auction, given that the starting price is 1900 euros.