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 is a medium level. This suggests that its value will not reach the highest prices seen in coins of better condition.

2. Previous Prices: By looking at previous auction prices for coins with a similar condition (75), we can see that they have reached hammer prices of up to 150 euros in recent auctions. For example, at the auction on 2020-10-21, a coin with a condition of 75 was sold for 150 euros.

3. Average Hammer Price: The average hammer price for this coin is 134.74 euros, which also provides a good reference point.

4. Starting Price: The current starting price is 90 euros, indicating that the seller expects a lower price than the average hammer price.

5. Sales Trends: The coin has been sold 94% of the times it has been auctioned, indicating good demand.

Based on these factors, an estimated maximum purchase price could be around 150 euros, as this is a price that has been reached in the past for coins of similar condition and aligns with the average hammer price. However, since the starting price is 90 euros, it is possible that it could be acquired for a price lower than this estimated maximum.

Therefore, a reasonable maximum purchase price could be 150 euros.