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. Auction History:
- The average hammer price for coins of this reference is 493.89 euros.
- In previous auctions, hammer prices have varied significantly, ranging from 170 euros to 1900 euros, depending on the condition and other factors.

3. Starting Price and Average Starting Price:
- The current starting price is 100 euros, which is lower than the average starting price of 166 euros. This could indicate an opportunity to purchase at a lower price.

4. Sales Trends: The coin has been sold in 9 out of the last 10 auctions, suggesting there is demand for this coin.

5. Previous Estimates: In past auctions, the estimated price has been significantly higher than the current starting price. For example, in a 2020 auction, the estimated price was 400 euros, and the hammer price was 1900 euros.

Based on these factors, an estimated maximum purchase price could be in the range of 400 to 600 euros, considering that the condition is 70 and there is a history of hammer prices exceeding 500 euros. However, since the starting price is 100 euros, it may be possible to acquire it for a lower price, but the mentioned range reflects the potential value of the coin based on its condition and auction history.

Therefore, a reasonable maximum purchase price could be 500 euros.