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

1. Starting Price: 750 euros.
2. Condition: The coin has a condition rating of 75 (MBC), indicating that it is in quite good shape.
3. Auction History:
- It has been auctioned 4 times in the past, of which it has sold 3 times.
- The average hammer price in previous auctions is 1050 euros.
- The previous hammer prices are:
- 900 euros (2018)
- 1300 euros (2015)
- No hammer price for 2014.

4. Average Starting and Hammer Price: The average starting price is 700 euros and the average hammer price is 1050 euros, suggesting that the coin tends to sell for above its starting price.

Given that the condition is good and the price history shows it has reached hammer prices of up to 1300 euros, we can estimate a maximum purchase price.

Considering all these factors, a reasonable maximum purchase price could be in the range of 1100 to 1300 euros, given that the average hammer price is 1050 euros and it has reached up to 1300 euros in the past.

Therefore, an estimated maximum purchase price could be 1200 euros.