To estimate a maximum purchase price for the coin in question, we can consider several factors based on the provided data:

1. Current Condition: The coin has a condition rating of 80 (MS+), which is quite good. This suggests that its value should be in the upper range of previous auctions.

2. Previous Auction Prices:
- The average hammer price for coins of similar condition (80) has been 114.38 euros.
- In previous auctions, hammer prices for coins with a condition of 80 have varied, but some examples are:
- 180 euros in December 2020.
- 150 euros in October 2020.
- 120 euros in January 2019.
- 295 euros in September 2017 (although this last one may be an exceptional case).

3. Current Starting Price: The starting price is 90 euros, indicating that the auctioneer expects moderate interest in the coin.

4. Sales Trends: The coin has been sold in 38 out of the last 45 auctions, indicating good demand.

5. Average Hammer Price: The average hammer price of 114.38 euros suggests that, in general, coins of this type tend to sell for above their starting price.

Based on these factors, an estimated maximum purchase price could be in the range of 120 to 150 euros, considering that the condition is good and that interest in the coin appears to be solid. However, since the highest hammer price in the past has been 295 euros, it is possible that in a competitive auction the price could exceed 150 euros, especially if there are several interested bidders.

Therefore, a reasonable maximum purchase price could be 150 euros, but be prepared for a potentially higher bid if demand is strong.