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

1. Current Condition: The coin has a condition of 75 (MBC), indicating that it is in fairly good shape, but not the best possible condition.

2. Auction History:
- In the past, the coin has been auctioned 4 times, of which it has sold 3 times.
- Previous hammer prices have been 1100, 1400, and 900 euros, with an average hammer price of approximately 1133.33 euros.

3. Current Starting Price: The starting price is 900 euros, which is slightly higher than the average starting price of 825 euros.

4. Price Trends:
- In the most recent auction (2024), the coin sold for 900 euros with a condition of 85, suggesting that the market is willing to pay around this price for coins in similar conditions.
- In previous auctions, hammer prices have been higher, especially when the condition was better (85 or above).

5. Maximum Price Estimate: Given that the current condition is 75, and considering that in previous auctions with similar conditions, hammer prices have reached up to 1100 euros, a reasonable maximum purchase price could be in the range of 1000 to 1100 euros. This is based on the fact that buyers may be willing to pay a little more than the most recent lower hammer price (900 euros) if demand is high.

Therefore, an estimated maximum purchase price for this coin could be approximately 1100 euros.