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 30 (BC+). This indicates that it is not in the best condition, which generally affects its value.

2. Auction History:
- The average hammer price for similar coins in the past has been 98.02 euros.
- Previous auctions of coins with a similar condition (30) have had hammer prices that vary, but are generally in the range of 15 to 40 euros.

3. Starting Prices and Estimates:
- The current starting price is 12 euros, which is relatively low.
- The average starting price for similar coins is 61.47 euros, suggesting there is potential for an increase in the hammer price.

4. Recent Trends: In the most recent auctions, hammer prices for coins with similar conditions have been in the range of 25 to 40 euros.

Based on these factors, an estimated maximum purchase price for this coin could be between 30 and 50 euros. This is because, although the condition is not high, the price history and recent auction trends suggest that there could be enough interest to reach that range.

Therefore, a reasonable maximum purchase price could be 40 euros.