I don't care if today is the expiry date; I want to buy it.
I don't mind if today's the expiry date, so I'll still buy it.
「今日が賞味期限でも構わないので購入したいです」は英語で「I don't care if today is the expiry date; I want to buy it.」と言います。「I don't mind if today's the expiry date, so I'll still buy it.」も言えます。「構わない」は「don't mind」と「don't care」でも大丈夫ですが、「don't care」のほうが少し冷たいと思います。
I don't care if today is the expiry date, so I want to buy it.
今日が賞味期限でも構わないので購入させてもらいたいです。
I don't care if today is the best before date. I'll buy it.
I want to buy it even if today is the best before date.
I don't care if today is the best before date. I'll buy it.
今日が賞味期限でも構いません。買います。
I want to buy it even if today is the best before date.
今日が賞味期限でも解体です。
best before date で「賞味期限」を英語で表現することができます。