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 80 (MS+), which is an acceptable level, but not among the highest. This may influence the price, as coins in better condition tend to fetch higher prices.

2. Starting Price and Historical Prices: The current starting price is 90 euros. Historically, the average hammer price for coins with a similar condition has been approximately 135-150 euros.

3. Sales Trends: Of the 45 times it has been auctioned in the past, it has sold on 34 occasions, indicating good demand. However, there is also a significant number of auctions where it did not sell, which may suggest that the starting price is an important factor.

4. Recent Hammer Prices: In the most recent auctions, hammer prices for coins with similar conditions have ranged from 110 to 170 euros.

5. Average Hammer Price: The average hammer price of 162.97 euros suggests that, under normal conditions, the coin could reach a higher price than the starting price.

Based on these factors, an estimated maximum purchase price could be around 150-170 euros, considering that the buyer might be willing to pay a bit more than the average hammer price, but not so much as to risk overpaying at an auction.

Therefore, a reasonable maximum purchase price could be 160 euros.