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

1. Current starting price: 300 euros.
2. Average hammer price in previous auctions: 365.96 euros.
3. Hammer price history:
- The coin has reached hammer prices of up to 500 euros in previous auctions, with grades of 100 and 95.
- In several auctions, the hammer price has been in the range of 300 to 500 euros, depending on the grade.

4. Grade: There is no information about the grade of this coin, which may affect its value. However, most coins of this type in the past have had grades of 95 or 100, which are quite high.

5. Price trends:
- The general trend shows that the hammer price can be significantly higher than the starting price, especially for coins in good condition.
- The average hammer price (365.96 euros) suggests that buyers are willing to pay more than the starting price.

Given that there is no information about the grade of this coin, but considering the price history and the average hammer price, an estimated maximum purchase price could be in the range of 400 to 500 euros. This is based on the fact that, although the grade is unknown, the price history suggests that buyers are willing to pay higher prices for similar coins.

Maximum purchase estimate: 450 euros.