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

1. Current Condition: The coin has a condition of 75 (MS), which is a medium level. This suggests that its value will not reach the highest prices seen in coins of better condition.

2. Auction History:
- The average hammer price for similar coins in condition 75 has been approximately 1,000 euros in previous auctions.
- In past auctions, hammer prices for coins with condition 75 have varied, with a maximum price of 1,775.51 euros in 2016.

3. Starting Price and Average Starting Price:
- The current starting price is 250 euros, which is relatively low compared to the average starting price of 487.2 euros. This suggests that there is potential for an increase in the hammer price.

4. Recent Trends: In the most recent auction, the coin sold for 550 euros, indicating that there is interest in the coin, but also that the market may be a bit more cautious.

5. Comparison with Previous Prices:
- The 2022 auction with condition 90 had a starting price of 713.33 euros, indicating that condition significantly affects the price.

Taking all these factors into account, an estimated maximum purchase price for the coin in condition 75 could be in the range of 800 to 1,000 euros. This is based on the historical hammer prices for coins of similar condition and the current interest in the coin.

Therefore, a reasonable maximum purchase price could be 1,000 euros.