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

1. Starting price: 350 euros.
2. Condition: 95 (S/C-), indicating good condition.
3. Auction history:
- It has been auctioned 3 times in the past, and it has sold every time.
- The average hammer price in previous auctions was 423.67 euros.
- The hammer prices in previous auctions were: 440 euros, 430 euros, and 401 euros.

Given that the coin is in good condition and has a history of successful sales, we can consider that the hammer price tends to be above the starting price.

### Analysis of previous prices:
- The highest hammer price was 440 euros.
- The lowest hammer price was 401 euros.
- The average hammer price was 423.67 euros.

### Estimation of the maximum purchase price:
Since the starting price is 350 euros and considering the history of hammer prices, a reasonable maximum purchase price could be in the range of 450 to 480 euros, taking into account that the coin is in good condition and that interest in the auction may drive up the price.

Therefore, an estimated maximum purchase price could be approximately 480 euros.