To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current starting price: 25 euros.
2. Current condition: 30 (BC+), indicating a low condition.
3. Auction history:
- In 2014, the coin was auctioned with a starting price of 90 euros and sold for 110 euros.
- In 2022, the starting price was 75 euros, with an estimated price of 100 euros, but it did not sell.

4. Average starting and final prices:
- Average starting price: 63.33 euros.
- Average final price: 77.5 euros.

Given that the current condition is quite low (30), this will negatively affect the estimated price. However, the auction history shows that in better conditions, the coin has reached significantly higher final prices.

Taking all these factors into account, an estimated maximum purchase price could be positioned between the average final price and the highest final price in the past, adjusted for the current condition.

Therefore, a reasonable maximum purchase price could be around 50-60 euros. This reflects a compromise between the price history and the current condition of the coin.