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

1. Current starting price: 500 euros.
2. Auction history: The coin has been auctioned 8 times and has sold on all occasions, indicating good demand.
3. Previous prices:
- The average hammer price in previous auctions is 391.25 euros.
- Hammer prices have varied, with a maximum of 460 euros in 2020 and 2023, and a minimum of 220 euros in 2019.
4. Condition: There is no specific information about the condition of the current coin, but in previous auctions, coins with conditions ranging from 80 to 95 have reached hammer prices between 220 and 460 euros.

Given that the starting price is 500 euros, which is above the historical average hammer price, and considering that the coin has a good sales history, we could estimate a maximum purchase price.

Estimation of the maximum purchase price:
- Based on the highest hammer price (460 euros) and the current starting price (500 euros), a reasonable maximum purchase price could be in the range of 450 to 500 euros, depending on the demand at the auction.

Therefore, an estimated maximum purchase price could be 450 euros. This allows for some margin for competition in the auction, while also staying within the limits of historical prices.