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

1. Current Condition: The coin has a condition of 75 (MBC), which indicates that it is in an acceptable state, but not among the best conditions. This can influence the price, as coins in better condition tend to reach higher prices.

2. Auction History:
- The average hammer price of similar coins in the past is 573.93 euros.
- The coin has had a hammer price of 810 euros in a previous auction with a condition of 90, indicating that coins in better condition can reach significantly higher prices.
- In recent auctions, hammer prices have varied, but there are examples of coins with similar conditions that have reached hammer prices of 480 euros (condition 70) and 280 euros (condition 75).

3. Starting Price: The starting price is 250 euros, which can be a good indicator of the seller's expectations, but not necessarily of the coin's actual value.

4. Market Trends: Since the coin has been auctioned 15 times and has had a high sales percentage (14 out of 15), this suggests that there is consistent interest in this coin.

Based on these factors, an estimated maximum purchase price could be in the range of 400 to 600 euros, considering that the current condition is 75 and that the average hammer price of similar coins is 573.93 euros.

Therefore, a reasonable maximum purchase price could be approximately 500 euros. This allows for competition in the auction and reflects the interest in the coin, as well as its condition.