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

1. 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 this coin in the past is 72.69 euros.
- The last auction where this coin was sold had a price of 90 euros, suggesting that there is growing interest or an increase in the coin's value.

3. Previous Starting and Hammer Prices:
- Hammer prices have varied, but there are examples of sales reaching up to 140 euros for coins of similar condition.
- The trend in hammer prices appears to be increasing, especially in the more recent auctions.

4. Current Starting Price: The starting price is 40 euros, which is relatively low compared to previous hammer prices.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 90 to 110 euros, given the recent interest and price history. This aligns with the average hammer price and the highest hammer price observed in the past.

Therefore, a reasonable estimated maximum purchase price would be 100 euros.