To estimate a maximum purchase price for the coin in question, we can analyze the provided data:

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

2. Auction History:
- The average hammer price in previous auctions is 355 euros.
- The hammer prices in past auctions have varied, ranging from 245 euros to 500 euros, depending on the condition of the coin in each case.

3. Current Starting Price: The starting price is 350 euros, which is slightly lower than the average hammer price.

4. Price Trends:
- In the most recent auctions, hammer prices have been higher, especially for coins in better condition (80 and 85).
- The trend seems to indicate that as the condition improves, the hammer price also increases.

Given that the condition of the coin is 75, which is an intermediate state, and considering the hammer price history, an estimated maximum purchase price could be set in a range that reflects both the condition and the price history.

Estimated Maximum Purchase Price:
We could consider a maximum purchase price of around 400 euros. This is based on the fact that the average hammer price is 355 euros and that, given the condition and interest in the coin, a buyer might be willing to pay a little more to secure the acquisition.