The price of bitcoin considerably dropped for some period.
The price of bitcoing drastically fell for a bit.
The price of bitcoin considerable dropped for a few days
「ビットコインの価格は一時期よりだいぶ下落した」は英語で「The price of bitcoin considerably dropped for some period.」と言えます。
同じ意味ですが、別の言い方で「The price of bitcoin drastically fell for a bit.」も言えます。
「一時期」は英訳すれば、「some period」や「a bit」と言えます。
もっと具体的な表現を使いたいなら、「a few days」でも使えます。これは「数日間」という意味です。そうすると、「The price of bitcoin considerable dropped for a few days」になります。
Bitcoin’s price has fallen a lot from where it was for a while.
Bitcoin’s price has fallen a lot from where it was for a while.
Bitcoin is down quite a bit from its earlier highs.
Bitcoin has dropped significantly from its peak.
Bitcoin is much lower than it was at one point.
「ビットコインの価格は一時期よりだいぶ下落した」は、英語では
1. 価格が下がった(fall / drop / be down)
2. どれくらい下がったか(a lot / quite a bit / significantly)
3. 一時期(at one point / for a while / earlier / from its peak / from its highs)
を組み合わせると自然です。