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

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

2. Auction History: The coin has been auctioned 9 times, of which it has sold 8. This suggests that there is consistent interest in the coin. The average hammer price in previous auctions is 51.63 euros, which can serve as a reference.

3. Starting and Hammer Prices: The current starting price is 150 euros, which is significantly higher than previous starting and hammer prices. However, the highest recorded hammer price was 138 euros in 2015, indicating that the current starting price might be a bit optimistic.

4. Price Trends: Looking at previous hammer prices, the range has varied, but the highest price was 138 euros. Given that the current condition is better than many of the coins auctioned previously, this could justify a higher price.

5. Final Estimate: Taking all these factors into account, an estimated maximum purchase price could be between 100 and 120 euros. This is based on historical interest, current condition, and the fact that the starting price is higher than previous hammer prices.

Therefore, a reasonable estimated maximum purchase price could be 120 euros.