To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current Condition: The coin has a condition of 70 (VF-), which indicates that it is in an acceptable state, but not excellent. This may influence the price, as coins in better condition tend to fetch higher prices.

2. Auction History:
- The average hammer price in previous auctions is 427.36 euros.
- The last auction for this coin had a hammer price of 420 euros with a condition of 80, which is better than the current one.
- In previous auctions, hammer prices have varied, but they have reached up to 750 euros in the case of a higher condition (85).

3. Starting Price: The current starting price is 300 euros, which is a reasonable starting point.

4. Price Trends: The overall trend shows that coins of this reference tend to sell above the starting price, especially in higher conditions.

Given all this, an estimated maximum purchase price could be in the range of 400 to 450 euros, considering that the current condition is lower than that of some coins that have sold in the past at higher prices. This also takes into account the average hammer price and the fact that the coin has a history of successful sales.

Therefore, a reasonable maximum purchase price could be approximately 450 euros.