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+), indicating that it is in quite good shape. This suggests that its value should be in the upper range of coins with a similar condition.

2. Previous Prices: Looking at previous auction prices for coins with a condition of 80, we can see that they have reached auction prices that vary, but generally range between 30 and 70 euros. For example:
- In previous auctions, coins with a condition of 80 have reached hammer prices of 40, 50, and even 70 euros.

3. Average Hammer Price: The average hammer price for this coin is 64.84 euros, which also indicates that the market value is in that range.

4. Starting Price: The starting price is 30 euros, which is reasonable, but given that the coin is in good condition, it is likely that the hammer price will be significantly higher.

5. Auction Trends: Since there have been 29 previous auctions and 28 sales, this indicates a consistent interest in the coin, which may increase its value in the current auction.

Based on these factors, an estimated maximum purchase price for this coin could be between 70 and 90 euros, considering that the condition is good and that interest in the coin has been consistent in the past. Therefore, a reasonable maximum purchase price could be 80 euros.