I'd like to spend as little money as possible on my trip.
I'd like to keep as tight a budget as possible when I travel.
MARIKOさんが教えてもらった英文ですが、次のように言うと良いですよ。
ーI'd like to spend as little money as possible on my trip.
または次のような言い方もできます。
ーI'd like to keep as tight a budget as possible when I travel.
「旅行するときはできるだけ予算を抑えたい」
to keep as tight a budget as possible「できるだけ予算を抑える」
ご参考まで!
I would like to go on a trip but at the same time would like to spend the least amount as possible.
ご質問ありがとうございます。
この場合、「私はできるだけ安く[旅行](https://eikaiwa.dmm.com/uknow/questions/44579/)に行きたい」と言いたいなら、英語で「I would like to go on a trip but at the same time would like to spend the least amount as possible.」という風に言えます。
ご参考になれば幸いです。