We should buy some land while the prices are still down.
It might be a good idea to purchase some property while it's still cheap.
この場合は during ではなく while を使います。
We should buy some land while the prices are still down.
「価格が下がっている内に土地を買うべきだ。」
while the prices are still down で「価格が下がっている内に」
It might be a good idea to purchase some property while it's still cheap.
「価格が安い内に土地を購入するのは良い考えだ。」
while it's still cheap で「価格が安い内に」
ご参考になれば幸いです！
日本 
