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+), indicating that it is in fairly good shape, but not of the highest quality (PRF).

2. Historical Prices:
- The average hammer price for coins of similar condition (80) has been approximately 280-280 euros in previous auctions.
- In past auctions, hammer prices for coins with a condition of 80 have ranged between 140 and 280 euros, with an average hammer price of 280 euros.

3. Starting Price and Average Hammer Price:
- The current starting price is 150 euros, which is relatively low compared to the average hammer price of 429.45 euros for all auctions of this coin.
- The average starting price of 270.79 euros also suggests that the current starting price is attractive.

4. Sales Trends: The coin has been sold 95% of the times it has been auctioned, indicating good demand.

Based on these factors, an estimated maximum purchase price could be around 280-300 euros, as this is the range where successful sales have occurred in the past for coins of similar condition. This also takes into account the current starting price and interest in the coin.

Therefore, a reasonable maximum purchase price could be 300 euros.