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

1. Coin Condition: The coin has a condition rating of 30 (BC+), indicating that it is not in very good shape. This generally reduces its value compared to coins in better condition.

2. Auction History:
- The average hammer price for similar coins in the past has been 90.71 euros.
- Previous auctions of this coin have shown hammer prices that vary significantly, ranging from 45 euros to 190 euros, depending on the condition and other factors.

3. Starting Price and Previous Prices:
- The current starting price is 60 euros, which is a good starting point.
- In previous auctions, the highest hammer price for coins with a similar condition (30) was 51 euros.

4. Price Trends:
- The overall trend seems to be that hammer prices have fluctuated, but the average hammer price of 90.71 euros suggests there is potential for an increase in price, especially if there is interest in the coin.

Taking all these factors into account, an estimated maximum purchase price could be around 70-80 euros. This is based on the fact that, although the condition is not high, the interest in the coin and the price history suggest it could reach a higher price than the current starting price. However, it is important to be cautious due to the condition.