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

1. Current Condition: The coin has a condition of 75 (MBC), which indicates that it is in an acceptable state, but not of the highest quality.

2. Auction History:
- It has been auctioned 12 times in the past, of which it has sold 9 times. This indicates good demand.
- The average hammer price in previous auctions is 92.09 euros, which gives us an idea of the value that buyers are willing to pay.

3. Previous Hammer Prices:
- Hammer prices for coins with a similar condition (75) have varied, but there are examples of auctions reaching up to 130 euros in the past.
- The lowest hammer price for a coin with a condition of 75 was 29.97 euros, indicating that the price can fluctuate quite a bit.

4. Current Starting Price: The starting price is 30 euros, which is quite low compared to the average hammer price.

Based on these factors, an estimated maximum purchase price could be in the range of 80 to 100 euros, considering that the average hammer price is 92.09 euros and that there are examples of higher hammer prices for coins in similar conditions.

Therefore, a reasonable maximum purchase price could be 100 euros.