Based on the provided data, we can observe that the coin in question has had starting prices in previous auctions of 100, 40, and 75 euros, with final prices of 102, 45, and no data provided in the last case. Additionally, it is indicated that the coin's condition is 30 (BC+).

Considering that the average final price has been 65.67 euros and the average starting price has been 66.67 euros, we can infer that the estimated purchase price could be around these values.

Given that the coin will be auctioned with a starting price of 25 euros and taking into account the previous prices as well as the coin's condition, we could estimate a maximum purchase price in the range of 70-80 euros. It is important to consider that factors such as demand at the time of the auction and competition from other bidders can influence the final purchase price.