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

1. Current condition: The coin has a condition of 75 (MBC), indicating that it is in quite good shape.

2. Auction history:
- The average hammer price in previous auctions is 23.67 euros.
- The hammer prices in previous auctions for coins with similar conditions (70 and 80) have varied, but it is observed that, in general, the hammer prices have been in a range of 15 to 40 euros, depending on the condition.

3. Starting and hammer prices:
- The current starting price is 15 euros, which is a reasonable price given the auction history.
- In previous auctions, the hammer price has reached up to 40 euros for coins with a condition of 80.

4. Trends:
- The general trend seems to be that coins with a condition of 75 can reach hammer prices in the range of 25 to 30 euros, based on the average hammer price and previous hammer prices.

Based on this information, an estimated maximum purchase price for the coin in question could be between 25 and 30 euros, considering that the condition is good and that the auction history supports this range.

Therefore, an estimated maximum purchase price could be 30 euros.