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 rating of 80 (MBC+), indicating that it is in relatively good shape. This suggests that its value could be in the upper range of previous auctions.

2. Previous Auction Prices: By looking at previous hammer prices for coins with similar conditions (around 80-85), we can see that the hammer prices have varied, but there are examples where they have reached up to 240 euros (as in the December 2020 auction).

3. Average Hammer Price: The average hammer price for this coin is 153.69 euros, which provides a good reference for the expected value.

4. Starting Price: The current starting price is 150 euros, which is reasonable and aligns with previous hammer prices.

5. Auction Trends: Given that the coin has been auctioned 27 times and all have sold, this indicates a consistent demand, which may drive up the hammer price.

Based on these factors, an estimated maximum purchase price could be in the range of 200 to 240 euros, considering that the condition is good and there are precedents for hammer prices in that range. Therefore, a reasonable maximum purchase price could be:

Estimated maximum purchase price: 240 euros.