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

1. Current starting price: 1100 euros.
2. Current grade: 80 (MBC+), which is a fairly good grade, although not the best.
3. Auction history: The coin has been auctioned 2 times in the past and has sold on both occasions. This indicates that there is demand for this coin.
4. Average starting and hammer price in the past: The average starting price has been 1150 euros and the average hammer price has been 1450 euros. This suggests that, in general, buyers are willing to pay more than the starting price.
5. Data from the previous auction: In the April 2022 auction, a coin with a grade of 85 sold for 1500 euros, indicating that a slightly better grade can significantly increase the hammer price.

Given that the current coin's grade is 80, which is lower than that of the previous auction (85), it is reasonable to adjust the expected hammer price downward. However, since the coin has a good sales history and there is interest in it, we can estimate a hammer price that reflects its value.

Taking all these factors into account, an estimated maximum purchase price could be around 1300-1400 euros. This is based on the fact that, although the grade is lower than that of the previous auction, the interest in the coin and its sales history suggest that it could reach a competitive price.