To estimate a maximum purchase price for the coin in question, we can 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. Auction History:
- The average hammer price for coins with a similar condition (80) in the past has been 80 euros (in the auction of 2018-05-31).
- In other auctions, the hammer price has varied, but the estimated price has consistently been higher than the starting price.

3. Starting Price and Average Hammer Price:
- The current starting price is 45 euros, which is reasonable given the history of starting and hammer prices.
- The average hammer price is 66.16 euros, suggesting that buyers are willing to pay more than the starting price.

4. Recent Trends: In the most recent auctions, hammer prices have shown a trend of being in the range of 80-120 euros for coins of similar condition.

Based on these factors, an estimated maximum purchase price for this coin could be between 80 and 100 euros, considering that the condition is good and that the price history suggests buyers are willing to pay more than the starting price.

Therefore, a reasonable maximum purchase price could be 100 euros.