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 85 (MBC+/EBC-), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Previous Prices: By looking at previous auction prices, we can see that the coin has reached auction prices of up to 420 euros in the past, although this was in an auction with unspecified condition. However, more recent auction prices for similar conditions (80-85) have been in the range of 150 to 340 euros.

3. Average Auction Price: The average auction price for this coin is 236.43 euros, providing a good reference for the expected value.

4. Starting Price and Average Starting Price: The current starting price is 175 euros, and the average starting price in the past has been 145 euros. This suggests that the current starting price is reasonable and could attract bidders.

5. Auction Trends: Since the coin has sold on all previous occasions and has had consistent interest, this suggests that there is solid demand.

Based on these factors, an estimated maximum purchase price could be in the range of 300 to 350 euros, considering that the condition is good and that interest in the coin appears to be high. This also aligns with previous estimated prices that have reached up to 400 euros in recent auctions.