Based on the provided data, we can observe that the coin in question has a conservation grade of 75 (MBC) and has had the following prices in previous auctions:

1. Auction on December 11, 2018:
- Starting price: 20 euros
- Estimated price: 25 euros
- Final price: 25 euros
- Conservation grade: 70

2. Auction on December 11, 2018:
- Starting price: 15 euros
- Estimated price: 25 euros
- Final price: 15 euros
- Conservation grade: 70

3. Auction on October 29, 2015:
- Starting price: 110 euros
- Estimated price: 200 euros

4. Auction on June 3, 2021:
- Estimated price: 9 euros
- Final price: 10 euros
- Conservation grade: 30

5. Auction on January 18, 2023:
- Starting price: 25 euros
- Estimated price: 40 euros
- Final price: 65 euros
- Conservation grade: 80

Considering that the average starting price is 39 euros and the average final price is 34 euros, and taking into account that the coin is in a conservation grade of 75 (MBC), we could estimate a maximum purchase price around 45-50 euros. It is important to note that the final price may vary depending on the demand at the auction and other external factors.