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

1. Condition: The coin has a condition of 70 (MBC-), indicating that it is in relatively good shape, but not of the highest quality (FDC).

2. Previous auction prices:
- In 2022, a coin with a condition of 80 was auctioned with a starting price of 35 euros and an estimated price of 45 euros. This suggests that as the condition improves, the price also increases significantly.
- In other auctions, hammer prices have varied, but they have generally been in a range of 24 to 35 euros for lower conditions (30).

3. Average hammer price: The average hammer price for similar coins is 27.5 euros, which can serve as a good indicator of market value.

4. Starting price and estimates: The current starting price is 18 euros, and the average starting price is 20.75 euros. This suggests that interest in the coin may be moderate.

Given that the condition of the coin is 70 and considering previous hammer prices, an estimated maximum purchase price could be in the range of 30 to 35 euros, taking into account that the condition is better than some coins that have sold in the past, but not high enough to reach the highest hammer prices.

Therefore, an estimated maximum purchase price could be 35 euros.