Della's problem in the story is raising the money she needs to purchase a suitable Christmas present for Jim.
The first step in her plan involves saving as much money as possible from the amount budgeted for household expenses. She manages to save $1.87 "by bulldozing the grocer and the vegetable man and the butcher until one's cheeks burned." This amount, however, would never be adequate, and so she needs to develop another step to her savings plan.
This is accomplished as Della takes action to raise funds by selling the one possession she has that would be worth the appropriate amount of money - her hair. Della decides to sacrifice this fabulous asset in order to achieve the goal of raising money for Jim's present.
she did it up again...Once she faltered for a minute and stood still while a tear or two splashed...With a whirl of skirts and with the brilliant sparkle still in her eyes, she fluttered out the door and down the stairs...Will you buy my hair?
In O. Henry's short story "The Gift of the Magi," Della plans on purchasing a Christmas gift for her husband Jim. Unfortunately, the couple's financial circumstances haven't left them in a place to be able to afford the extravagance of exchanging presents.
Della had tried to save money for this purpose as best she could by putting away a cent at a time when she was purchasing their groceries; however, this technique only left her with one dollar and eighty-seven cents.
Thus, in an act of self-sacrifice and love, Della decides to sell her most prized possession: her hair. She lets Mrs. Sofronie cut it all off in exchange for twenty dollars, and she uses the money to purchase a gold watch chain for Jim.
The irony of this, of course, is that we shortly thereafter learn that Jim has sold his own most prized possession--his watch--in order to afford a set of beautiful combs for Della's hair. Although the couple's presents are ultimately useless, they are an incredible testament to their selflessness.