To estimate a maximum purchase price for the coin in question, let's consider the following factors:

1. Current starting price: 300 euros.
2. Coin condition: 100 (S/C), indicating it is in excellent condition.
3. Auction history: The coin has been auctioned once before, with an estimated price of 50 euros and a hammer price of 36 euros, but with a condition of 85, which is lower than the current one.
4. Average hammer price: 36 euros, which is significantly lower than the current starting price.

Since the condition of the current coin is much better than that of the previous auction, this could justify a higher price. However, the average hammer price of 36 euros suggests that the market is not willing to pay much more for this coin, even in good condition.

Taking these factors into account, an estimated maximum purchase price could be positioned between the starting price and the average hammer price. Given that the condition is excellent, we might consider a maximum purchase price around 100-150 euros, reflecting a balance between the quality of the coin and the price history in the market.

Therefore, the estimated maximum purchase price would be approximately 150 euros.