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 relatively good shape, but not of the highest quality (FDC).

2. Auction History:
- The average hammer price for similar coins has been 185.58 euros.
- In previous auctions, hammer prices have varied significantly, ranging from 40 euros to 420 euros, depending on the condition and demand at that time.

3. Starting Price and Average Starting Price:
- The current starting price is 90 euros, which is below the average starting price of 103.93 euros. This could indicate a buying opportunity.

4. Sales Trends:
- Of the 15 times it has been auctioned in the past, it has sold 12 times, suggesting there is consistent interest in this coin.

5. Recent Hammer Prices:
- In the most recent auction with a similar condition (75), the hammer price was 220 euros.

Based on these factors, an estimated maximum purchase price could be in the range of 180 to 220 euros, considering that the average hammer price is 185.58 euros and there is interest in coins of similar condition.

Therefore, a reasonable maximum purchase price could be 200 euros. This allows for competition in the auction and aligns with previous hammer prices.