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 indicates that it is in quite good shape. This suggests that its value should be in the upper range of coins with a similar condition.

2. Previous Prices: Looking at previous auction prices for coins with a similar condition (80), we have:
- 2019-01-24: Hammer price 170
- 2022-12-14: Hammer price not available, but the starting price was 250.
- 2023-03-16: Hammer price 180
- 2023-05-24: Hammer price not available, but the starting price was 175.

The highest hammer price for a condition of 80 was 180, and the lowest was 170.

3. Average Hammer Price: The average hammer price for previous auctions is 208.33, indicating that, in general, coins of this reference tend to sell for above 200 euros.

4. Current Starting Price: The starting price is 150 euros, which is relatively low compared to previous hammer prices.

5. Auction Trends: The coin has been auctioned 11 times, of which 9 have sold. This indicates good demand and consistent interest in the coin.

Based on these factors, an estimated maximum purchase price could be set in a range between 180 and 220 euros, considering that the highest hammer price for a similar condition was 180 euros and that the average hammer price is 208.33 euros.

Therefore, a reasonable estimated maximum purchase price could be 200 euros. This allows for a margin for competition in the auction, given that the starting price is 150 euros.