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

1. Current Condition: The coin has a condition of 80 (MS+), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History:
- The average hammer price of similar coins in the past is 55.93 euros.
- The last auction of a coin with a similar condition (80) had a hammer price of 100 euros.
- In previous auctions, hammer prices have varied, but there are examples of sales reaching up to 100 euros for similar conditions.

3. Starting Price and Average Starting Price: The starting price is 50 euros, and the average starting price of similar coins is 42.33 euros. This suggests that the starting price is reasonable and could attract bidders.

4. Sales Trends: The coin has been sold in 14 out of the last 15 auctions, indicating a consistent interest in this reference.

Based on these factors, an estimated maximum purchase price could be in the range of 90 to 120 euros, considering that the condition is good and there are precedents for high hammer prices in previous auctions.

Therefore, a reasonable maximum purchase price could be 100 euros.