To estimate a maximum purchase price for the coin in question, we can analyze the provided data and consider several factors:

1. Current Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History:
- In the past, the coin has been auctioned 5 times, and all have sold, indicating consistent demand.
- Previous hammer prices have varied, but the highest was 92.24 euros in 2015 with a condition of 75, and 90 euros in 2020 with a condition of 80.

3. Current Starting Price: The starting price is 120 euros, which is significantly higher than previous hammer prices. This may indicate that the seller expects an increase in value, possibly due to the condition or current demand.

4. Average Hammer Price: The average hammer price of 70.25 euros suggests that, in general, coins of this reference have sold for a price lower than the current starting price.

5. Market Trends: Given that the condition of the coin is better than some of the previous auctions, it is reasonable to assume that it could reach a higher price than previous hammer prices, but not necessarily the starting price.

Taking all these factors into account, an estimated maximum purchase price could be between 90 and 100 euros, considering that the condition is good and there is a history of hammer prices that supports this estimate. However, given the starting price of 120 euros, it is possible that some bidders may be willing to pay a bit more, but it would be wise not to exceed 100 euros to ensure a reasonable purchase.