Based on the information provided, we know that the coin will be auctioned for the first time and its condition is 25 (BC). Since there are no previous auction data for this coin, we can try to estimate a maximum purchase price based on the condition and the starting price.

Given that the condition is 25 (BC), indicating a fairly low condition, the starting price is likely a good reference point to establish a maximum purchase price. However, keep in mind that being an auction, the final price may vary depending on demand and other factors.

Therefore, in this case, we could consider a maximum purchase price close to the starting price, so an estimated maximum purchase price could be around 18 euros. It is important to note that this is just an estimation and the final price could be different at the auction.