That ultra expensive kit is the Development kit. I remember I was interested in programming for GBA systems a long time back and I took a look at it. The reason it's so expensive is it comes with a 512 megabyte flash card.

If I understand correctly, you just want the cable so you can back up your games to your computer and transfer them to the device right?

hmmm wow my bad... I looked into this a year or so ago and I found them everywhere for between $12 and $20. Now there doesn't seem to be one to be had for love or money :/

EDIT: However, the one you linked to should definitely do what you want it to.