To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially the previous auction prices and the current condition of the coin.

1. Current Condition: The coin has a condition of 75 (MS), indicating that it is in fairly good shape, but not the best possible condition.

2. Previous Auction Prices: Looking at the auction prices of coins with similar conditions:
- Condition 70: Auctions of 175, 190, 170, 121 (in different auctions).
- Condition 80: Auctions of 195, 210, 340, 240 (in different auctions).
- Condition 85: Auctions of 460 (in different auctions).

3. Average Auction Price: The average auction price for coins auctioned in the past is 261.75 euros, which gives us a good reference.

4. Starting Price: The current starting price is 180 euros, which is slightly lower than the average auction price.

5. Trends: Given that the coin has sold in all previous auctions and considering that the auction price can vary depending on demand, an auction price around 200-250 euros seems reasonable, given that the condition is 75.

Maximum Purchase Price Estimate: Based on the previous information, a maximum purchase price that could be considered reasonable would be between 220 and 250 euros, taking into account the condition and previous auction prices.

Therefore, an estimated maximum purchase price could be 250 euros.