Taking the bullet train costs twice as much as regular trains, but it's twice as fast too.
Taking the bullet train is more than twice the price of any regular train, but it cuts your travel time in half as well.
この場合、次のように言うと良いでしょう。
ーTaking the bullet train costs twice as much as regular trains, but it's twice as fast too.
「新幹線は普通電車の２倍の値段だが、２倍速くもある」
to cost twice as much as ... で「２倍の値段がかかる」
twice as fast で「２倍速い」
ーTaking the bullet train is more than twice the price of any regular train, but it cuts your travel time in half as well.
「新幹線は普通電車の２倍の値段だが、（電車に乗っている）時間は半分になる」
more than twice the price で「値段は２倍以上」
to cut one's travel time in half で「旅行時間を半分にする」
ご参考まで！
Taking the bullet train is twice as expensive but it takes less than half the time.
The Shinkansen is twice as expensive but twice as fast too.
こんにちは。
様々な言い方ができると思いますが、例えば以下のような英語表現はいかがでしょうか：
Taking the bullet train is twice as expensive but it takes less than half the time.
新幹線は2倍の値段ですが、時間は半分以下です。
The Shinkansen is twice as expensive but twice as fast too.
新幹線は2倍の値段がしますが、はやさも2倍です。
twice as expensive - 2倍の値段
twice as fast - 2倍はやい
ぜひ参考にしてください。
カナダ 
アメリカ合衆国 
