To estimate a maximum purchase price for the coin in question, we can analyze 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. Historical Prices: By looking at the hammer prices of similar coins in the past, we can see that the hammer prices have varied considerably. For example, in previous auctions, coins with similar conditions have reached hammer prices ranging from 60 to 140 euros, depending on demand and other factors.

3. Starting Price and Average Hammer Price: The current starting price is 90 euros, and the average hammer price for similar coins is 132.25 euros. This suggests that there is potential for an increase in the hammer price.

4. Recent Trends: In the most recent auctions, hammer prices have shown a trend of being higher, especially for coins with superior conditions. However, since this coin has a low condition rating, it is likely that its hammer price will not reach the highest levels.

5. Estimated Price Analysis: The estimated prices in previous auctions for coins with similar conditions have been around 100 to 150 euros.

Based on these factors, an estimated maximum purchase price for this coin could be around 110-130 euros, considering that the condition is a limiting factor. This would allow for a competitive bid without exceeding the expected market value.