It's cheaper to buy in bulk.
大批购买便宜些。
The company seems to be doing so well that I would like to buy in.
这家公司看起来生意兴隆，我愿意入股。
He will buy in as a partner.
他将入股成为股东。
It is usually economical to buy washing powder in large quantities.
大量购买洗衣粉通常要省钱些。
Many farmers buy in ewes in autumn.
许多牧场主在秋天大批买进母羊。