It's cheaper to buy in bulk.

大批购买便宜些。

Buying in bulk is more economical than shopping for small quantities.

大批采购比少量购买更经济实惠。

Storekeepers buy them in bulk and resell them for $150 each.

店主大批买进这些，又以每件$150的价格转卖出去。

And they often bought bulbs in bulk to save money.

并且，他们常常大批购买灯泡来省钱。

Buy in bulk.

批量购买。