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

1. Current Condition: The coin has a condition rating of 30 (BC+), which indicates that it is not in the best condition. This generally negatively affects its value compared to coins in better condition.

2. Auction History:
- The average hammer price for this coin in the past has been 111.38 euros.
- However, the hammer prices for coins with a similar condition (30) have been significantly lower. For example, in previous auctions, the hammer prices for coins with a condition of 30 have ranged from 15 to 25 euros.

3. Starting Price and Average Starting Price:
- The current starting price is 12 euros, and the average starting price in the past has been 45.61 euros. This suggests that the current starting price is quite low compared to the historical average.

4. Recent Trends: In the most recent auctions, the hammer prices for coins with a condition of 30 have been around 25 euros, indicating that interest in coins in this condition may be stabilizing in that range.

Based on these factors, an estimated maximum purchase price for this coin could be between 20 and 30 euros, considering that the condition is not optimal and that interest in coins of this quality may limit the final price.

Therefore, a reasonable maximum purchase price could be 25 euros.