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

1. Coin 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. Auction History: By looking at previous hammer prices for coins with similar conditions, we can see that:
- In past auctions, coins with a condition of 80 have reached hammer prices of up to 150 euros (for example, in the auction on 2018-10-17).
- The average hammer price for coins of similar condition seems to be in the range of 60 to 150 euros.

3. Average Hammer Price: The average hammer price for this coin is 75.81 euros, which is also a good indicator of the expected value.

4. Starting Price: The starting price is 45 euros, suggesting that there is considerable room for the hammer price to be higher.

5. Recent Trends: In the most recent auctions, hammer prices have shown a trend of increasing, especially for coins in good condition.

Based on these factors, an estimated maximum purchase price for this coin could be between 120 and 150 euros, considering that the condition is good and there is a history of hammer prices that supports this estimate.

Therefore, a reasonable maximum purchase price could be 150 euros.