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+), indicating that it is in relatively good shape. This suggests that its value should be above that of coins in worse conditions.

2. Auction History:
- The average hammer price for similar coins in the past is 20.13 euros.
- Previous hammer prices for coins with a similar condition (80) have varied, but there are examples of hammer prices in the range of 15 to 30 euros.
- The last auction with a condition of 80 had a hammer price of 20 euros.

3. Starting Price and Average Starting Price:
- The current starting price is 12 euros, which is quite low compared to the average starting price of 24.64 euros. This suggests that there is potential for the hammer price to be significantly higher.

4. Price Trends:
- In previous auctions, coins with a condition of 80 have reached hammer prices of up to 30 euros.

Based on these factors, an estimated maximum purchase price for this coin could be in the range of 25 to 30 euros, considering that the condition is good and that the price history suggests it could reach that level in an auction.

Therefore, a reasonable estimated maximum purchase price would be 30 euros.