Brain Game. Shopping Woman

Lots of Shopping BagsToday here’s a new riddle about a shopping woman. I hope, you will like and solve it.
“How much does 1 cost?” asked the customer at a shop.
“$20.” answered the shop assistant.
“And how much are 12?” asked the woman again.
“$40.” was the answer.
“In fact I need 120.”
“Here you are. $60, please.”

What was the woman buying?

Please, if you want to solve the riddle yourself, be careful and do not look at the comments of this post, because someone could have already written the solution there. Good luck! You will find the answer in the next brain game. You are always welcome to ask questions about the task, in case something is not clear. But sorry, I will not answer leading questions.

The answer to the previous brain game is: make a group of 10 coins and a group of 40 coins. Then, turn each of the 10 coins over. This will make two groups with the same number of heads up. Anybody, Andrew, Al Kinsley, Joseph Smith (StillUnashamed) gave the right solution. Very well done! Now try the new one.