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

1. Current Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in an acceptable state, but not among the best qualities.

2. Auction History:
- The average hammer price in previous auctions is 237.15 euros, suggesting that, in general, coins of this reference tend to reach higher prices.
- The last auction in January 2023 had a hammer price of 340 euros, indicating significant interest in this coin, especially in similar conditions.

3. Starting and Hammer Prices:
- The current starting price is 90 euros, which is relatively low compared to previous hammer prices.
- The average starting price in past auctions is 109.55 euros, suggesting that the current starting price is in line with expectations.

4. Sales Trends:
- Out of the 7 times it has been auctioned, it has sold 6 times, indicating a good sales rate and demand.

5. Proximity of the Auction: There is an auction scheduled in the coming days, which may increase interest and competition among bidders.

Based on these factors, an estimated maximum purchase price could be in the range of 250 to 300 euros, considering historical interest and the most recent hammer price. This would allow a buyer to be in a competitive position without exceeding the market value observed in previous auctions.