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

1. Current Condition: The coin has a condition of 20 (Fair), indicating that it is in quite poor condition. This will negatively affect its value compared to coins in better condition.

2. Auction History:
- Previous hammer prices for coins of the same reference and in better conditions (70 to 95) have varied considerably, with hammer prices ranging from 700 to 1600 euros.
- The average hammer price for coins in superior conditions is approximately 1165.71 euros.

3. Starting Price and Average Starting Price:
- The current starting price is 480 euros, which is significantly lower than the average starting price of 1105 euros for similar coins.

4. Sales Trends: The coin has been auctioned 10 times, of which it has sold 8 times, indicating good demand, although the current condition may limit interest.

5. Condition-Based Estimation: Given that the condition of this coin is quite low (20), it is reasonable to assume that its hammer price will be below the average of previous hammer prices.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 300 to 500 euros. This is based on the need to adjust the value downward due to the condition, but also considering that the starting price is 480 euros, which suggests there may be interest in the auction.

Therefore, a reasonable maximum purchase price could be approximately 450 euros.