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

1. Coin Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in quite good shape.

2. Auction History:
- The average hammer price for coins with a similar condition (80) has been approximately 45 euros in previous auctions.
- The last auction of a coin with a condition of 80 had a hammer price of 65 euros.

3. Average Starting and Hammer Prices:
- The average starting price is 20.75 euros, and the average hammer price is 38.47 euros. This suggests that coins tend to sell for a price higher than the starting price.

4. Price Trends:
- In previous auctions, hammer prices for coins with a condition of 80 have varied, but the range has been from 30 to 100 euros, depending on demand and other factors.

5. Current Starting Price: The starting price is 5 euros, which is quite low compared to previous hammer prices.

Based on this data, an estimated maximum purchase price for the coin could be in the range of 60 to 80 euros, considering that the condition is good and that the hammer price history for similar coins supports this estimate.

Therefore, a reasonable maximum purchase price could be 70 euros.