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 rating 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 for coins of this reference is 661.43 euros.
- In previous auctions, hammer prices have varied considerably, ranging from 420 euros to 1400 euros, depending on the condition.
- The last auction with a similar condition (75) had a hammer price of 400 euros.

3. Starting Price and Estimates:
- The current starting price is 400 euros, which is a reasonable starting point.
- The estimated price for this auction is 700 euros, suggesting that there are expectations for the coin to reach a higher price.

4. Sales Trends:
- Out of the 9 times it has been auctioned, it has sold 7 times, indicating good demand for this coin.

Based on these factors, an estimated maximum purchase price could be positioned in a range between the average hammer price and the estimated auction price. Given that the condition is 75, and considering the price history, a reasonable maximum purchase price could be:

Estimated maximum purchase price: 600 euros.

This price takes into account the current condition and the price history, as well as the sales trend of the coin.