Based on the provided data, we can see that the coin in question has a grade of 70 (MBC-), indicating that it is in fairly acceptable condition. Additionally, it has been auctioned three times in the past, selling each time.

The starting price for the next auction is 30 euros, and the average selling price in previous auctions has been 53.33 euros. We can also observe that in the last auction, the coin sold for 30 euros, suggesting there is interest at that price.

Taking into account this data, as well as the previous prices of the coin (15 euros and 25 euros), and considering the grade of 70 (MBC-), we could estimate a maximum purchase price around 35-40 euros. Since the starting price is 30 euros and the average selling price is 53.33 euros, it is reasonable to expect the coin to sell for a price close to these values, so an offer of up to 40 euros could be considered as an estimated maximum purchase price.