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

1. Starting Price: 30 euros, which is the initial price of the auction.
2. Current Condition: 25 (BC), indicating that the coin is in quite low condition. This generally negatively affects the final price.
3. Auction History: In the past, this coin was auctioned with a condition of 70, reaching a final price of 220 euros. This suggests that in better condition, the value could be significantly higher.
4. Average Final Price: 220 euros, which is the average price that has been reached in previous auctions for this coin.

Given that the current condition is quite low (25), it is reasonable to expect that the final price will be below the average of 220 euros. However, since there has been interest in this coin (it has sold in the past and has not gone unsold), we can estimate a final price that reflects its condition.

Taking all these factors into account, an estimated maximum purchase price could be between 50 and 80 euros. This is based on the idea that, although the condition is low, there is a history of interest and a previous final price that suggests there may be buyers willing to pay more than the starting price.

Therefore, a reasonable maximum purchase price could be 70 euros.