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 in a fairly deteriorated state. This will negatively affect its value compared to coins in better condition.

2. Previous Auction Prices:
- The coin has been auctioned 7 times, and all have been sold.
- Previous hammer prices varied significantly, but the highest (with conditions of 80 and 95) reached prices of 260 and 1800 euros, respectively.
- The price trend shows that coins in better condition (80 and 95) have a significantly higher value than those in lower condition.

3. Starting Price and Average Price:
- The current starting price is 90 euros, which is relatively low compared to the average starting price of 215 euros and the average hammer price of 430 euros.

4. Condition-Based Estimation:
- Given that the condition of this coin is 30, it is reasonable to assume that its value will be below the hammer prices of coins in better condition.
- Considering that coins with a condition of 70 have reached hammer prices of up to 130 euros, and that a condition of 30 is significantly lower, an estimated hammer price could be in the range of 30 to 70 euros.

5. Conclusion:
- Taking all these factors into account, an estimated maximum purchase price for this coin could be around 70 euros, as this price reflects its condition and the price trend in previous auctions.

Therefore, the estimated maximum purchase price would be 70 euros.