As expressed by the others in the thread, it's $8. Cars are expensive, car audio is expensive.
Is it expensive for what it is? Probably.
Could you fabricate something similar yourself for cheaper? Possibly.
You could probably rig up something similar yourself and literally save yourself a few bucks, but it wouldn't be anywhere near as elegant. Unless you consider your time worthless I'd suggest buying it.
Hell, I paid like three times that (~$22) at a local car audio shop for a wiring harness before I learned they could be found cheaper at Walmart. I knew I could probably find one even cheaper online, but it was the only thing missing and I was impatient.