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 (MBC+). This is an important factor, as coins in better condition tend to reach higher prices.

2. Auction History:
- In the past, coins of the same reference with condition ratings of 90 and 85 have been auctioned, reaching hammer prices of up to 380 euros.
- The last auction with a condition rating of 85 had a hammer price of 380 euros, indicating that there is a market willing to pay high prices for well-preserved coins.

3. Average Hammer Price: The average hammer price for similar coins is 231.33 euros, suggesting that, in general, buyers are willing to pay more than the starting price.

4. Starting Price: The starting price is 70 euros, which may attract more bidders, but does not necessarily reflect the true value of the coin.

5. Auction Trends: Since it has been auctioned 4 times in the past and sold 3 of those times, there is a consistent interest in this coin.

Based on these factors, an estimated maximum purchase price could be between 300 and 400 euros, considering that the condition is slightly lower than the coins that have reached higher prices, but there is still significant potential for value.

Therefore, a reasonable maximum purchase price could be 350 euros.