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

1. Current Condition: The coin has a condition rating of 70 (MS-). This is an important factor, as coins in better condition tend to reach higher prices.

2. Previous Auction Prices:
- The average hammer price in previous auctions is 320.36 euros.
- The last auction with a similar condition (70) had a hammer price of 240 euros.
- In previous auctions, hammer prices for coins with a condition of 70 have varied, but they have sold for over 200 euros on several occasions.

3. Current Starting Price: The starting price is 225 euros, which is a reasonable starting point.

4. Sales Trends: The coin has sold in 12 out of the last 16 auctions, indicating a consistent interest in the coin.

5. Average Starting Price: The average starting price of 236.88 euros suggests that the current starting price is in line with market expectations.

Given all this, an estimated maximum purchase price could be in the range of 300 to 350 euros, considering that the average hammer price is 320.36 euros and that the coin's condition is a key factor. However, since the condition is 70, a more conservative price might be around 300 euros, while a more optimistic buyer might be willing to pay up to 350 euros.

Therefore, a reasonable estimated maximum purchase price would be approximately 300-350 euros.