You can buy a 5kg bag of rice for 3,000 yen or a 1kg bag for 1,000 yen, which is a poor buy relatively speaking.
この場合、次のような言い方ができますよ。
ーYou can buy a 5kg bag of rice for 3,000 yen or a 1kg bag for 1,000 yen, which is a poor buy relatively speaking.
「5キロのお米を3,000円か1キロのお米を1,000円で買えるけど、1キロのお米の方が割高です」
a poor buy「割高」
relatively speaking「比較して言うと」
ご参考まで！
カナダ 
