To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current Condition: The coin has a condition rating of 80 (MS+), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Current Listing Price and Previous Prices: The current listing price is 150 euros, and the average hammer price in previous auctions has been 191.43 euros. This suggests that the hammer price tends to be higher than the listing price.

3. Sales History: The coin has been auctioned 51 times, of which it has sold 48 times. This indicates good demand and sustained interest in the coin.

4. Previous Hammer Prices: Looking at previous hammer prices for coins with a similar condition (80), we can see that they have reached hammer prices of up to 800 euros in the past, although this was in an exceptional case. Most hammer prices for similar conditions have been in the range of 150 to 260 euros.

5. Recent Trends: In the most recent auctions, hammer prices have been in the range of 180 to 240 euros for similar conditions.

Based on these factors, an estimated maximum purchase price could be in the range of 220 to 250 euros. This is based on the history of hammer prices and the current condition of the coin. Therefore, a reasonable maximum purchase price could be 250 euros.