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

1. Current starting price: 120 euros.
2. Coin condition: 75 (MBC), indicating good but not excellent condition.
3. Previous auction prices:
- In 2019, the coin was auctioned with a starting price of 90 euros and sold for 120 euros, with a condition of 80.
- In 2014, the starting price was 300 euros and it sold for 420 euros, although the condition is not specified.
- In 2021, the estimated price was 600 euros and it sold for 750 euros, with a condition of 85.

4. Average hammer price: 460 euros, which is significantly higher than the current starting price.

Given that the condition of the current coin is 75, which is lower than the conditions of the coins that have sold in the past (80 and 85), it is reasonable to expect that the hammer price will not reach the highest levels observed.

However, the average hammer price of 460 euros suggests that there is a market willing to pay higher prices for coins in good condition.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 300 to 400 euros, considering that the condition is not the best and that the starting price is relatively low. A price of 350 euros could be a reasonable target, as it falls in the middle of this range and reflects moderate interest in the coin.