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:
- The average hammer price for similar coins in the past is 513.33 euros.
- The last auction of a coin with a similar condition (80) had a hammer price of 400 euros.
- In previous auctions, hammer prices have varied significantly, ranging from 200 to 1200 euros, depending on the condition and other factors.

3. Starting Price and Estimated Price:
- The current starting price is 350 euros, which is slightly higher than the average starting price of 330.77 euros.
- The estimated hammer price for this auction has not been provided, but considering the history, it could be in a range similar to the average hammer price.

4. Market Trends: Given that the coin has been auctioned 13 times and has had a high sales percentage (12 out of 13), this indicates a consistent interest in the coin, which may influence the price.

Based on these factors, an estimated maximum purchase price could be in the range of 500 to 700 euros, considering that the condition is good and that the hammer price history suggests that coins in similar conditions have reached higher prices in the past.

Therefore, a reasonable maximum purchase price could be 650 euros.