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

1. Starting Price: 200 euros. This is the initial price set for the auction.

2. Auction History:
- It has been auctioned 4 times in the past, of which it has sold 3 times.
- The average starting price in previous auctions is 116.25 euros, and the average hammer price is 153.33 euros.
- In previous auctions, the hammer prices have been 100 euros (with a grade of 75) and 140 euros (with a grade of 75), indicating that the price may vary depending on the grade.

3. Current Grade: The coin has a grade of 80 (MBC+), which is better than the grades of 75 in previous auctions. This suggests that the hammer price could be higher than previous prices.

4. Price Trends: Given that the starting price is 200 euros and considering that in the last auction a hammer price of 200 euros was estimated (although it has not sold yet), this suggests an expectation that the price may reach or exceed this value.

Taking all these factors into account, an estimated maximum purchase price could be in a range between the starting price and the average hammer price of previous auctions, adjusted for the better grade of the coin.

Estimated Maximum Purchase Price: 180 - 220 euros.

This is based on the expectation that, due to the better grade, the price could be at the upper end of the range. However, it is important to note that the market can be unpredictable, and collector interest may also influence the final price.