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

1. Current Condition: The coin has a condition of 75 (MBC), which indicates that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History:
- The average hammer price in previous auctions is 54.26 euros.
- In past auctions, the hammer price has varied, with a maximum of 96 euros in a recent auction (2020-10-27) for a coin with a condition of 70.
- Coins with a condition of 80 have reached hammer prices of up to 80 euros.

3. Starting Price and Estimated Price:
- The current starting price is 50 euros, which is a good starting point.
- The estimated price of 100 euros in previous auctions suggests that there is potential for a higher hammer price.

4. Sales Trends: The coin has been sold in 25 out of 27 auctions, indicating good demand.

Based on these factors, an estimated maximum purchase price could be in the range of 80 to 100 euros, considering the current condition and the hammer price history. A price of 90 euros could be a reasonable target, given that it has been reached in previous auctions and the condition of the coin is quite good.