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 30 (BC+), indicating that it is not in very good shape. This generally negatively affects its value compared to coins in better condition.

2. Starting Price and Historical Prices: The current starting price is 70 euros. The average hammer price in previous auctions is 148.89 euros, suggesting that, in general, coins of this reference tend to sell for higher prices than their starting price.

3. Sales Trends: Out of the 42 times it has been auctioned, 37 have been sold, indicating a good sales rate. However, the highest hammer price in the past for coins with a similar condition (30) is 85 euros (observed in the auction on 2018-05-30).

4. Comparison with Previous Prices: In previous auctions, coins with similar conditions have had hammer prices ranging from 45 to 85 euros. This suggests that, given the current condition, the hammer price could be in the lower range of this spectrum.

5. Final Estimate: Taking all these factors into account, an estimated maximum purchase price for this coin could be between 70 and 85 euros, with 85 euros being a reasonable upper limit given the price history and current condition.

Therefore, an estimated maximum purchase price could be 85 euros.