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 to be auctioned has a condition of 75 (MBC), indicating that it is in quite good shape. This is relevant because coins in better condition tend to fetch higher prices.

2. Previous Auction Prices:
- Previous hammer prices for coins with similar conditions (70 and 80) range from 110 to 345 euros.
- The average hammer price for past auctions is 262.78 euros, suggesting that, in general, coins of this reference tend to sell above their starting price.

3. Starting Price and Average Starting Price:
- The current starting price is 125 euros, which is below the average starting price of 176.43 euros. This could indicate potential for an increase in the hammer price.

4. Sales Trends: Since all coins of this reference have sold in the past, this suggests a consistent demand.

5. Estimation Based on Condition and Previous Prices:
- Given that the coin's condition is 75, and considering that coins with conditions of 70 have reached hammer prices of up to 345 euros, we can estimate that the hammer price for this coin could be in a similar or slightly higher range, given that its condition is better.

Based on these factors, an estimated maximum purchase price for the coin could be between 300 and 350 euros, considering that the condition is favorable and there are precedents for hammer prices in that range.

Therefore, a reasonable maximum purchase price could be 350 euros.