To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially previous auction prices and conditions.

1. Current starting price: 450 euros.
2. Average auction price in the past: 369.35 euros.
3. Previous auction prices:
- The highest auction prices in recent auctions are 550 euros (on several occasions).
- The condition of the coins auctioned in those cases was 95, which is a high condition.

4. Condition of the current coin: No information is provided about the condition, which can be an important factor. However, since there have been recent auctions with conditions ranging from 80 to 95 that have reached auction prices of up to 550 euros, we can infer that the price could be in a similar range if the condition is good.

5. Price trends: Noticing that the auction price has been increasing in recent years, especially for coins in good condition, we can consider that interest in this coin may have grown.

Given all this, an estimated maximum purchase price could be in the range of 500 to 550 euros, assuming the coin has an acceptable condition and that interest in the auction is high. Therefore, a reasonable maximum purchase price could be:

Estimated maximum purchase price: 550 euros.