To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Condition: The coin has a condition rating of 100 (MS), indicating that it is in excellent condition. This generally increases its value compared to coins with lower conditions.

2. Previous auction starting and hammer prices:
- The average starting price in previous auctions is 619.23 euros, and the average hammer price is 704.6 euros.
- In previous auctions, the hammer price has varied but has reached up to 950 euros in a recent auction.

3. Sales trends: Out of the 13 times it has been auctioned, it has sold 10 times, indicating good demand for this coin.

4. Hammer prices in previous auctions:
- In auctions with similar condition (100), the hammer prices have been 600, 950, and 800 euros, suggesting that the price can fluctuate quite a bit but tends to be in the range of 600 to 950 euros.

5. Current starting price: The starting price is 600 euros, which is a reasonable starting point.

Considering all these factors, an estimated maximum purchase price could be in the range of 800 to 950 euros, as this is a price that has been reached in previous auctions and reflects the good condition of the coin.

Therefore, a reasonable maximum purchase price could be 950 euros.