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 similar coins in the past has been 138.59 euros.
- In previous auctions, coins with a similar condition (80) have reached hammer prices that varied, but some examples are:
- 125 euros in December 2020.
- 265 euros in February 2020.
- 190 euros in March 2014.

3. Starting Price and Average Starting Price:
- The current starting price is 40 euros, which is quite low compared to the average hammer price.
- The average starting price for similar coins is 77.19 euros.

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

Based on these factors, an estimated maximum purchase price could be in the range of 150 to 250 euros, considering that the condition is good and that the price history shows that similar coins have reached higher prices in the past.

Therefore, a reasonable maximum purchase price could be 200 euros.