To estimate a maximum purchase price for the coin in question, we will 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. Previous Auction Prices:
- The average hammer price for similar coins in the past has been 669.22 euros.
- In previous auctions, hammer prices have varied significantly, ranging from 200 euros to 1600 euros, depending on the condition and other factors.

3. Starting Price and Average Starting Price:
- The current starting price is 300 euros, and the average starting price in previous auctions is 382.92 euros.

4. Sales Trends: Out of the 13 times it has been auctioned, it has sold on 10 occasions, indicating good demand.

5. Comparison with Prices of Similar Condition: In recent auctions, coins with a condition of 75 have reached hammer prices of 420 euros (on two occasions) and 500 euros.

Based on this data, an estimated maximum purchase price could be in the range of 500 to 700 euros, considering that condition is an important factor and that the average hammer price has been 669.22 euros.

Therefore, a reasonable maximum purchase price could be approximately 600 euros. This allows for a margin for competition in the auction and aligns with previous hammer prices for coins of similar condition.