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

1. Starting Price: 60 euros. This is the initial price of the auction.
2. Condition: The coin has a condition of 30 (BC+), indicating that it is not in very good shape. This may affect its value compared to coins in better condition.
3. Auction History: The coin has been auctioned once in the past, with a starting price of 80 euros and a hammer price of 120 euros. This suggests that, despite its condition, there is interest in the coin that could lead to a higher hammer price.
4. Average Starting and Hammer Prices: The average starting price is 70 euros and the average hammer price is 120 euros. This indicates that, in general, coins of this reference tend to sell for higher prices.

Given that the coin has a condition of 30, it is likely that its hammer price will not reach the historical maximum of 120 euros, but it could be in a lower range. Considering the starting price of 60 euros and the demonstrated interest in the previous auction, an estimated maximum purchase price could be between 80 and 100 euros.

Therefore, a reasonable estimated maximum purchase price for this coin could be 90 euros. This takes into account its condition and the historical interest in the coin.