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

2. Starting Price and Average Hammer Price: The current starting price is 1200 euros, and the average hammer price in previous auctions is 1331 euros. This suggests that, in general, coins of this reference tend to sell above the starting price.

3. Auction History:
- In previous auctions, we have seen hammer prices that varied, but some have reached up to 1900 euros (in 2018 with a condition of 85).
- The trend of hammer prices for coins with similar conditions (80) has been in the range of 1300 to 1450 euros on several occasions.

4. Comparison with Previous Prices:
- The last auction with a condition of 85 reached a hammer price of 1750 euros, indicating that a slightly better condition can significantly increase the price.
- The most recent auction with a condition of 80 had a hammer price of 1400 euros.

Based on these factors, an estimated maximum purchase price for the coin with a condition of 80 could be in the range of 1400 to 1600 euros. This is based on the history of hammer prices and the trend of previous auctions.

Therefore, a reasonable estimated maximum purchase price could be 1500 euros.