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

1. Current Condition: The coin has a condition rating of 75 (MBC), indicating that it is in quite good shape. This can positively influence its value.

2. Auction History:
- The coin has been auctioned 10 times, of which it has sold 8 times. This suggests there is consistent interest in the coin.
- The average hammer price in previous auctions is 29.86 euros, providing a good reference for its market value.

3. Previous Prices:
- In recent auctions, the coin has reached hammer prices of up to 63 euros (in an auction with a condition of 80) and 35 euros (in an auction with a condition of 75).
- The current starting price is 20 euros, which is relatively low compared to previous hammer prices.

4. Price Trends:
- The average starting price in previous auctions is 34.6 euros, indicating that the current starting price may be underestimated.

Taking all these factors into account, an estimated maximum purchase price could be between 40 and 50 euros, considering that the condition is good and there is a history of hammer prices that supports this estimate.

Therefore, a reasonable maximum purchase price could be 45 euros.