Given:

A desktop computer which lacks the wireless capability.

To find: The least expensive ways to upgrade the system with the wireless capabilities.

Solution:

Following are the two least expensive ways:

Install the wireless expansion card in the system.

Connect a USB wireless adapter through a USB port.

Both the above options are cheaper than buying a new desktop or trading the computer with another person, as extra money might be required to compensate for a wireless system, and not to mention the hassle of trading.

Hence, the options C and D are the least expensive ways to upgrade the system with the wireless capabilities.