To estimate a maximum purchase price for the coin in question, let's consider several factors:

1. Current starting price: 200 euros. This is the initial price set for the auction.
2. Condition of the coin: 80 (MBC+). This indicates that the coin is in good condition, which may increase its value.
3. Historical data: In the previous auction, the coin was offered with a starting price of 50 euros and was sold for 70 euros. This suggests that interest in the coin may have increased since then, as it is now being offered at a higher starting price.
4. Average starting and final prices: The average starting price is 125 euros and the average final price is 70 euros. This indicates that, in general, coins of this reference tend to sell for below their starting price.

Given that the condition of the current coin is better than that of the previous auction and considering the increase in the starting price, an estimated maximum purchase price could be positioned between the current starting price and the average final price of the previous auction.

Taking all these factors into account, an estimated maximum purchase price could be around 150 euros. This reflects moderate interest, considering the condition and auction history, but also acknowledges that the current starting price is significantly higher than previous prices.