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 (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 similar coins in condition 80 has been 57.66 euros.
- In previous auctions, hammer prices for coins with condition 80 have varied, reaching up to 110 euros in the best cases (as in the auction on 2018-04-25).

3. Starting Price and Average Starting Price:
- The current starting price is 45 euros, which is reasonable given the history of starting and hammer prices.
- The average starting price of 38.03 euros suggests that the current starting price is competitive.

4. Sales Trends: The coin has been sold in 33 out of the last 40 auctions, indicating good demand.

5. Previous Estimates: In past auctions, the estimated price has been up to 150 euros for coins in similar condition, although this may be an extreme value.

Based on these factors, an estimated maximum purchase price could be in the range of 80 to 100 euros, considering that the condition is good and that the hammer price history supports this estimate. Therefore, a reasonable maximum purchase price could be 90 euros.