Based on the provided data, the coin in question has a starting price of 18 euros and has been auctioned twice in the past, selling on both occasions. The conservation of the coin is described as "BC+" (30 on a conservation scale of 0 to 110).

Additionally, information is given about a previous auction of the same coin, which took place on April 28, 2022. On that occasion, the coin had a starting price of 18 euros, an estimated price of 30 euros, and finally sold for 35 euros. The conservation rating of the coin in that auction was 25.

Given that the average selling price in previous auctions was 30 euros, and considering that the conservation of the coin is relatively good (BC+), we could estimate a maximum purchase price around 35-40 euros. However, keep in mind that the final price in an auction can vary depending on demand and other market factors at the time of the auction.