To estimate a maximum purchase price for the coin in question, we can analyze the provided data:

1. Current starting price: 30 euros.
2. Average hammer price in previous auctions: 42.5 euros.
3. Current condition: 30 (BC+), which is a moderate condition.
4. Auction history:
- In 2014, it was auctioned with a starting price of 30 euros and sold for 60 euros.
- On the same date, another similar coin was auctioned with a starting price of 12 euros and sold for 25 euros.
- In 2022, it was auctioned with a starting price of 20 euros and was estimated to sell for 35 euros, although it did not sell.

Given that the current condition of the coin is 30 (BC+), which is better than the 25 in the 2022 auction, and considering that in the past it has reached a hammer price of 60 euros, we can infer that the hammer price could be in a higher range.

Estimation of the maximum purchase price:
- Based on the average hammer price of 42.5 euros and the highest hammer price of 60 euros, a reasonable maximum purchase price could be between 50 and 60 euros, considering that condition is an important factor and that the market can fluctuate.

Therefore, an estimated maximum purchase price could be 55 euros.