To estimate a maximum purchase price for the coin in question, we can consider several factors based on the provided data:

1. Current starting price: 110 euros.
2. Coin condition: 70 (MBC-), which indicates an acceptable but not excellent condition.
3. Auction history:
- In 2015, the coin was auctioned with a starting price of 175 euros and sold for 900 euros, indicating high interest and possible overvaluation at that time.
- In 2020, the starting price was 20 euros, but the final bid was only 25 euros, suggesting that interest in that auction was low.
- In 2024, the coin is expected to have a starting price of 600 euros and an estimated price of 900 euros, suggesting that interest has increased again.

4. Average final bid price: 462.5 euros, which is a good indicator of the value that buyers are willing to pay.

Given that the coin has a very variable auction price history, but with an average final bid price of 462.5 euros, and considering that the condition is 70, an estimated maximum purchase price could be set in a range that reflects both current interest and auction history.

Taking all these factors into account, an estimated maximum purchase price could be around 400 to 500 euros. This is based on the interest shown in previous auctions and the average final bid price, adjusted for the current condition of the coin.